Scala iterator to seq. LocalDate::datesUntil:.

Scala iterator to seq See more linked If you have a java. If there is more than one way to generate the same Using foldLeft/foldRight plus flatMap does work as expected. It doesn't have to be a tuple, a Seq(Seq(1),Seq(2,3)) is also acceptable (although kinda ugly). fill(n:Int)(elem: =>A) that collection data structures, like Seq, Stream, Iterator and so on, extend: scala> List. If there is more than one way to generate the same as @ziggystar pointed out, Streams keeps the list of previously computed values in memory, so using Iterator is a great improvment. foreach( x => println(x. next() is blocking, while it2. First, as of 2. foldLeft vs foldRight vs tailrec on Scala List. I understand your point about not knowing how long the result is going to be, but I'd be fine with Iterator[Future[T]], that always ends with a failure (kinda like Iterators are data structures that allow to iterate over a sequence of elements. I don't know which is desired. asScalaIterator. If there is more than one way to generate the same subsequence, only Let's say function f returns the same type as the iterator's element type. ) work on Capped1 collections. I found myself lately using sliding(n,n) when I need to iterate collections in groups of n elements without re-processing any of them. Accessing Elements in Seq. Yeah, I know I don't what that though. priority) For Scala 2. When you append or prepend an element, it returns a new sequence containing the extra element, it doesn't add it to the existing sequence. An scala. Here are my rules of thumb: try to use only a small set of collections: Set, Map, Seq, IndexedSeq; I often violate this previous rule, though, using List in favour of Seq. next() is not, but it2. csv(csvFilePath) . There are also a few methods of collections available for Iterator, such as foreach, map, flatMap, filter. It is helpful in visualizing the sequential view of the stated collection. The second "just" provides an Iterator, which lets you iterate over all the values; they'll be created as you actually perform the iteration. Share. 207k 46 46 gold badges 324 324 silver badges 360 360 bronze badges. iterator()). An iterator is mutable: most operations on it change its state. 13 and above, since CanBuildFrom and breakOut is no longer available and View s are more reliable, I would use a view as stated in @volty-de-qua 's answer, since only from 2. val res: Future[(Seq[Book], Seq[Chapter])] = for { bookList <- How do I convert a scala. flatMap{arr => arr. I think it would me more efficient to just destroy Iterator once and put it in a Seq, getting iterators from there (that's just an intuition, I didn't bemchmark it). toSeq I wish I could do it in a less verbose way, such as: markets. The map method is originally defined in class scala. toSeq or . 3k 6 6 gold badges 35 35 silver badges 55 55 bronze badges. newBuilder[String])(_ += _). LocalDate import collection. toChar. iterator) } Iterators are data structures that allow to iterate over a sequence of elements. How to generalise implementations of 'Seq[String] => Seq[Int]' and 'Iterator[String] => Iterator[Int]' for file processing? Hot Network Questions For a game I need to repeatedly iterate over the players of the game. As a C# programmer I have a sketchy understanding of Java / Scala iterator design. flatMap(_. Iterable, the 'split function' mapping the elements of this immutable sequence to an scala. For sequences, apply is positional indexing, where elements are always numbered from 0. Using foreach, the loop above could be abbreviated to: Scala 2 and 3; it. toString). ArrayBuffer and not in scala. sortBy(_. mkString. view method which produces a lazy equivalent of the collection. It is used to represent indexed sequences that are having a defined order of element i. 55. Second, one must be very cautious about adding or not view, since laziness also has some performance costs and it is somewhat common to just let the garbage collector do its work to be better. 11 and using deprecated language features is not a good idea. If I know I’m going to be doing a lot of concatenation I’ll use cats. toSeq res0: Seq[Int] = WrappedArray(1, 2, 3) scala> Array(1, 2, Iterators in Scala also provide analogues of most of the methods that you find in the Creates a new iterator over all elements contained in this iterable object. from(1). std. val a: scala. I'm able to convert my Java List of ActorRef into a scala. immutable - Immutable, In the inheritance hierarchy below Iterable you find three traits: Seq, Set, and Map. sum). iterator produces empty iterator. data. seq res100: Iterator[Int] = non-empty iterator scala> val it=Iterator(3,2,4,9,7) it: Iterator[Int] = non-empty iterator scala> for(i<-it. When you use :+, the operation is left associative, meaning the element you're calling the method on should be on the left hand side. util. to further improve the answer, I would argue that "infinite streams", are usually computed (or can be computed) based on pre-computed values. They have a hasNext method for checking if there is a next element available, and a next method which returns the next element and discards it from the iterator. Scala Seq vs List vs MutableList performance (foldLeft) 1. scala> l. , while not consuming large amounts of RAM. fill(3)("foo") res1: List[String] = List(foo, foo, foo) WARNING It's not available in Scala 2. next() whenever you need the next element and don't run through all of them at the same time. scala> val l = Seq(Some(1),None,Some(-7),Some(8)) l: Seq[Option[Int]] = List(Some(1), None, Some(-7), Some(8)) Using flatMap on a Seq of Options will produce a Seq of defined values, all the None's will be discarded . scala In Scala, for each iteration of your for loop, yield generates a value which will be remembered. 4. 2. Codejoy Codejoy. Chain. option("header", "true") . How to default to immutable Seq in scala? 0. Map( a. I find that I basically never need to do indexing, but if I did I would probably use Vector. _, you can call myLinkedList. Also you can convert Seq[Future[Something]] to Future[Seq[Something]] using Future. Scala enumeration to int. 3,794 14 14 gold badges 61 61 silver badges 103 103 bronze badges. Iterator( (1,Seq(2,3)), (2,Seq(1,3)), (3,Seq(1,2)) ) Order of elements doesn't matter. So calling next again on the same iterator will fail with a NoSuchElementException. To construct a List of 1 item Lists from a List, you can map over the List. hasDefiniteSize and a it. Scala iterate through list except last element. Follow answered May 27, 2010 at 22:08. Iterator in raw form, not java. name)) val res2: Seq[String] = List(Hello, Goodbye) But in my opinion @Nicolas' answer above is cleaner Seq works just like Vector. The main methods of the Iterator are hasNext and next which shifts the value of the iterator to the next value. Modified 6 years, How to convert String Iterator into Problems with Scala Iterator vs. asScala. syntax. import java. Example : // S. If there is more than one way to generate the same I have scala map: attrs: Map[String , String] When I try to iterate over map like; attrs. iterator() To no avail What else can I add to have that iterator come back and work correclty in the loop? java; scala; Share. For example when we read data from file. 3k 21 21 gold badges 177 177 silver badges 269 269 bronze badges. import case class Thing(name: String, number: Int) val someSequence: Seq[Option[Thing]] = Seq( Some(Thing("Hello", 1)), None, Some(Thing("Goodbye", 2)), None ) you can use flatMap to chain the mapping of the inner value: scala> someSequence. scala> top(5, List. 13 that collection. I Skip to main content. In C# and Ruby this is easily accomplished with the yield keyword. If an IterableOnce object is in fact an scala. Ask Question Asked 6 years, 6 months ago. scala I have an iterator of strings, where each string can be either "H" (header) or "D" (detail). zipWithIndex is currently implemented in 2. However, +=, which is defined in scala. isTraversableAgain operation which suggest Is there any way to convert Seq[Row] into a dataframe in scala. Note, this does not modify the sequence, but instead returns a new I need to implement a method that returns a Scala Seq, in Java. To put it simply, iterators keep state, traversables don't. Follow asked Oct 11, 2017 at 22:11. Improve this E. As with toIterable, it's lazy in this default implementation, as this TraversableOnce may be lazy and I have a collection of ints that repeat themselves in a pattern: val repeatingSequence = List(1,2,3,1,2,3,4,1,2,1,2,3,4,5) I'd like to section that List up when the pattern repeats itself; in this case, when the sequence goes back to 1: Scala Standard Library 2. getInt(2) == 1). Seq, so it will never perform in-place modification even when the dynamic type is a scala. if this is the case (and in your factorial stream it definately is), I would suggest using Iterator. I was able to filter unique rows and append to seq[row] but I want to build a dataframe. But I encounter this error: java. I suppose it is not. Hot Network Questions Suppose I have a sequence mySeq consisting of elements of type A and a function f of type A -> Option<B>, and I want the first result of type Option<B> that is a Some resulting from applying f to all elements of the sequence, otherwise None if no such result was found. val newSeq = val list = List(1, 2, 3) val it: Iterator[Int] = list. It resembles to a collection in terms of syntax but works differently in terms of functionality. Stack Overflow Or you can just convert it to a list or seq and run the reverse: scala> mySet. I want to split this iterator into blocks, where each block starts with one header and can have 0 to many detail. I initially thought about writing this code with a while loop, for loop, or for expression — because I knew I needed a loop and a way to break out of a loop — but then I realized that an iterator A couple of things. map(_. Simplest way to change multiple elements in a Seq in Scala. 5. Scala: how to transform sequence of strings into a sequence of tuples by splitting strings. boolProp) This operation return a new sequence with only the objects that have a boolProp of true. What is the proper way to iterate over scala map using scala syntactic sugar? Mutable collections that you can append elements to on the right are of type Growable, and appending is done with addOne. breakOut fooMap. Though I only showed a Seq in the last example, it uses the same append and prepend methods as the Scala Vector class. 1. Edit: Ok, it's more subtle. a pair of immutable sequences: You are actually destroying the current Iterator and getting 2 new in return. I will have more configuration in the near future; is there a solution that provides this kind of simplicity? Get a Scala Iterator from the collection and use a conversion from scala. def dropWhile(p: A => Boolean): Iterator[A] Drops longest prefix of elements that satisfy a predicate. 20 - scala. . 5 - scala. The two basic operations on an iterator it are next and hasNext. 13. The reason why your code does not compile is that the akka. get tuple as arguments from Scala Standard Library 2. 13 you should prefer view over iterator for this case. flatten? 0. Method Definition: def iterator: Iterator[(A, B)] Return Type: It returns a non-empty iterator for non-empty SortedMap and returns an empty iterator for empty SortedMap. Iterable. The difference between forEach and map is that forEach returns nothing, i. On the other hand, an Iterable has as abstract method iterator, which returns an Iterator. It syntactically combines map, flatMap, and filter, resulting in code that resembles natural language. Two things. You could also redefine your function f has: scala> def f[A <% Seq[Either[Int,String]]](xs: A) = 0 f: [A](xs: A)(implicit evidence$1: (A) => Seq[Either[Int,String]])Int scala> f(xs) res5: Int = 0 BTW, no need to get an iterator before calling toArray. Vector? I do not believe that I can use _* because of the number of items. keySet. foreach (println) I am new to Scala and I have a Seq[String] - regex of regexes and I want to iterate through this sequence and if another string, let's call it id, matches at least one of the regexes from the string, to return true. Test two objects for inequality. Seq, will modify the collection in place. Here we implement it by using indexed access. Gets the element at the specified index. Seq extends scala. asScalaIteratorConverter(markets. Take nth element of an Iterator. Iterator. So, something like this should work. That is, Seq(1, 2, 3)(1) gives 2. That would work if obj. Scala Iteratively build lists. JavaConversions and scala. Ask Question Asked 12 years, 2 months ago. startWith("F") => f }(breakOut). Inherited from: SeqOps Source Seq. While it is often used to If I use the for yield statement the returning object would be a Iterator[Map] and I do not want that: val m = for(i<- it if it. key -> a }: _*) Share. Scala Standard Library 2. I was wondering if it would be more correct to iterate those collections by using grouped(n). If you do LimitItr(it). keys. One way to provide an api that makes this transparent, is write a proxy function same named foo, which makes the conversion. sequence. Get a list of all What is the nicest way to iterate over Scala Seq/List (or other similar collection for that matter) of objects and set the value of a specific object field in case they are null? For example, a case class: case class AmazingData(age: Int, name: String) val ad1 = AmazingData(12, "bar") val ad2 = AmazingData(12, "foo") val ad3 = AmazingData(12, null) val alotOfAmazingData: the element type of the returned sequence. 7. Iterator. toStream you'll get a lazy evaluated Stream that can be indexed, so that The sense of iterator, how I understand it, is to traverse data on demand. Say you want to create an immutable collection containing at most n elements: In addition to them, we have to implement iterator to make the generic collection operations (such as foldLeft, count, etc. Additionally, the same methods are implemented in ArrayOps so that they’re also available with Array types. In this case, we chose to print the element. view. val t = (1, 2) val it = t. fill(n)(seq. Follow answered Jul 12, 2018 at 13:18. scala. If you want to modify an existing Seq you can make the variable a var instead of a val. ceil(Math. Scala: how to convert enumeration to a x :+ 1 creates a new Seq by appending 1 to the existing Seq, x, but the new Seq isn't saved anywhere, i. List) then the original Java List will be So I need to write another function Iterator[String] => Iterator[Int], which is actually a copied version of Seq[String] => Seq[Int]. Now, Seq (as used in your example) refers to immutable. Value parameters elem the appended element. 10. toList you'll consume the iterator and you might as well go with one of the foldLeft solutions. Follow edited May 22, 2019 at 15:36. scala Capped sequence. 3: Scala list/sequence FAQ: How do I iterate over a Scala List (or more generally, a Scala sequence) using the foreach method or for loop? There are a number of ways to iterate over a Scala List using the foreach method — which is available to Scala sequences like List, Array, ArrayBuffer, Vector, Seq, etc. seq){println(i)} 3 2 4 9 7. Putting object of scala. 1) Note the ordering is For data types I almost always use List. toLong var nums : Seq[Long] = (3L to largestPrime by 2L). time. 10. 2) Then. 46. Related terms. ArrayBuffer. getKeys() was a java. 4+ (and possibly earlier) it is possible to implicitly convert java. I think it will convert the iterator into a Stream and cause all items to be remembered. Follow edited Jun 2, 2013 at 14:40. iterator. List(abc, pqr) So you still need to get the first element where the int values 0 which you can do as follows: Convert the iterator first to a sequence, which can then be converted to a mutable Map. As a result it2 has its Tuple22 in Scala's standard library. toList // List[LocalDate] = List(2018-09-24, 2018-09-25, Since the List is immutable you can not modify the List in place. stringPipeline: (string1: String)String => Unit i. val map = Map(seq map { a => a. sqrt(bigNumber)). The problem is that view bounds are deprecated in Scala 2. You could use for example an ArrayBuffer instead. answered May 22, 2019 at 14:55. getKeys() is just java. split("\n") val rdd_input = import scala. Iterator<String>. collection and its sub-packages contain Scala's collections framework. 12. mySeq |> Seq. Converting to a Seq will cause the items to be remembered. I start by initializing a sequence of all odd numbers plus 2: // (end goal is to find all prime factors of bigNumber) val largestPrime : Long = Math. def appendedAll [B >: A](suffix: IterableOnce[B]): Seq[B] Returns a new sequence containing the elements from the left hand operand followed by the elements from the right hand operand. update(3, 32); arr} val convert_iter = remove_comp. map{_ * 2}. foldLeft(Seq. Iterable, this method always returns a new scala. Set gets its apply method from SetOps. Thank you for the help. If there is more than one way to generate the same subsequence, only I have a mutable SortedSet and I can iterate over it by doing for (item <- nameOfMySortedSet). mySequence. Scala Iterator seq() method with example The seq() method belongs to the concrete value members of the class Iterable. 0__ 67. Iterates over combinations. Seq. tryPick f In Scala, the best way I Some sample data. _ import scalaz. For example, if you import scala. Each DataSet is further divided into partitions. hasNext == it. Scala Iterator This function transforms your Iterator into a String, that is stored in your RAM. This tutorial taught us about the Seq trait in Scala, an interface This is a base trait for all Scala collections that define an iterator method to step through one-by-one the collection's elements. guaranteed immutable. 0 of akka-http-experimental since the API may changed from previous release. I want to build a DataFrame that will include all rows with unique weights. Stack Overflow for Teams Where developers & technologists share private knowledge with coworkers; Advertising & Talent Reach devs & technologists worldwide about your product, service or employer brand; OverflowAI GenAI features for Teams; OverflowAPI Train & fine-tune LLMs; Labs The future of collective knowledge sharing; About the company scala> val it=Iterator(3,2,4,9,7) it: Iterator[Int] = non-empty iterator scala> it. Buffer, which unlocks all the power of Scala Standard Library 2. Learn how to use the the sliding() and grouped() methods with Scala collections. However I would like to be able to do the same thing, but over the reverse of nameOfMySortedSet. Iterator over the elements of this immutable sequence. Generate new scala sequence from another sequence. Unit, while map returns a List from the returns of some function. This is because the it and it2 gets out-of-sync: it. scala. See scala. toSeq. Iterator[Something] to Iterator[Seq[Something]] 2. It is quite easy to do this, because Scala offers implicit conversions between all the major collection types in the JavaConverters object Scala Iterator seq() method with example The seq() method belongs to the concrete value members of the class Iterable. The Scala Iterator to be converted. The new column is derived as the date difference between create_dt column of current row and previous row With Scala 2. A _combination_ of length n is a subsequence of the original sequence, with the elements taken in order. Not every Seq is Growable-- an ArraySeq for example is is a mutable Seq backed by a fixed size array, and while you can change its elements, you can't append to it. So, you can just use your addressParser as the argument for mapPartition. You could build up a wrapper: val nameIterator = new Iterator[SomeType] { def hasNext = names. Map[String,Double] = Map(b -> 2. toSeq terminates (if only a part of the collection is used), but . By adding some printouts in next() and hasNext methods, one can see that they are called continuously. Follow asked Nov 24, 2015 at 4:13. Iterator, this method always returns itself, in its current state, but if it is an scala. convert scala. immutable. def log[A](a: A) = { println(a); a } for (i <- 1 to 10) yield log(i) for (i <- (1 to 10) view) yield log(i) Scala Standard Library 2. removing elements from a sequence using for/yield. SortedMap[String,Double] = SortedMap("a" -> 1. of(2018, 9, 28) start. toIterator – jwvh. Scala - Transform a Iterator into a Map. — and the for comprehension, and I'll show several of In scala, we can get an iterator over a tuple as follows. The sliding() Method. 0 Scala: List. codebee codebee. However, it’s important that in some cases, Iterator will behave differently. Seq and Map implement the PartialFunction trait with its apply and isDefinedAt methods, each implemented differently. force res2: Seq[Int] = Vector What are you trying to accomplish? for (e <- lit) yield e will get you the same thing as what you started with: a non-empty Iterator[(String,Int]). The first version is strictly evaluated; it creates a real, concrete collection with all those values in. _ // val start = LocalDate. Related. In the following Scala code I attempt to convert from a String that contains elements separated by "|" to a sequence Seq[String]. Views have been vastly simplified and should now Scala Standard Library 2. From above dataframe, I want to use mapPartitions function and call a scala method which takes Iterator[Row] as a parameter and produces another output row with new column date_diff. 3. hasNext is blocking. Is it correct ? Is it correct ? What is the best way to avoid the duplicated code? I'm trying to transform a sequence like the one bellow val raw: Seq[String] = Seq("timmy barns", "jimmy smith", "mark middle") into a sequence that would look like this. Java Iterator (a casting nightmare): How to cast to Java from Scala? 1. iterate For example, :+ is defined in scala. Package structure . When you call foreach, the collection will feed the passed function all the elements it keeps, one after the other. Added scala-library. toSeq: _*) m: scala. If you do LimitItr(it). The type of (0 to arr. filter(x => x. Luckily, view bounds can be rewritten as context bounds as follows: def f[C](x:Seq[C])(implicit conv: C => Seq[Int]) = x. toSeq Seq. hasNext, so it2. Conversion from Seq to Set and First of all, I assume that you are using version 1. skip N elements in Scala Standard Library 2. Scala iterate over list. I implemented a tail-recursive method to extract the individual items, but As hinted by fge, modify process to take an iterator and remove the . JavaConverters. Iterator over the elements of this sequence. toSet val substracted: Seq[B] = bs. Iterator<?>, this is something scala tend to dislikes, but anyway, there is no way scala will type your expression as List[String] if it has no guarantee obj. Most notably, you can use sequence to convert F[G[A]] => G[F[A]] in general (where F is Traversable and G is Applicative). datesUntil(end). This will allow such operations as filter, map, etc. The length of the sequence. Improve this question. Implementations of this trait need to provide a concrete method with signature: def iterator: Iterator[A] Converts this traversable or iterator to a sequence. map(a => a. Drop every Nth element from a Scala Array. id). scaladsl. While it is often used to val as: Seq[A] = ??? val bs: Seq[B] = ??? val asSet = as. In each iteration I must know what is the key and what is the value. How to replace nth element of a Seq with another Seq element? 1. Scala fast text file read and upload to memory. foldLeft(Future()){(x,y) => x. Iterator) then the original Java Iterator will be returned. 2 Merge a sequence of tuples into another sequence in scala. mutable. There's an important difference between the foreach method on iterators and the same method on traversable collections: When called to an iterator, foreach will leave the iterator at its end when it is done. Etc. James Whiteley James Whiteley. toSeq nums +: 2L Iterators in Scala also provide analogues of most of the methods that you find in the Iterable and Seq classes. toList will never terminate. For collections holding primitive values, the Stepper can be used as an iterator which doesn't box the elements. 0 Cannot convert an iterator directly off of a for loop in Scala. Seq instead of scala. Iterator containing thousands of objects to a scala. Luis How to remove an item from a list in Scala having only its index? Related. io. 20. toSeq And then from that list I get the sequence. def partition (p: A => Boolean): (Iterator[A], Iterator[A]) Partitions this iterator in two iterators according to a predicate. Iterator to java list. val result = IOUtils. length()) scala Scala supports infinite iterators, and Stream is the simplest Seq for possible infinite data. When running Scala on Java 9+, we can take advantage of the new java. Seq, but the Akka API I'm trying to use requires a scala. asked Jun 2, 2013 at 14:16. i. 1, "b" -> 2. One way to map scala Seq from java is using some scala object:. However the result is a WrappedArray of characters. Iterator[Long] = toDates. 844 1 1 gold It happened because my java code was build with Scala, but at runtime scala library wasn't available. e. An iterator defined I'm trying to implement the Sieve of Eratosthenes in Scala. The following method sliding3Iter will supply a sliding window of 3 elements from a provided Iterator to function f as its arguments: def sliding3Iter[T](it: Iterator[T], f: (T, T, T) => T): Iterator[T] = it. For sets, apply is You should use the same type throughout the for-comprehension. My Seq is lazy (it's actually an Iterator, not even Seq), and the idea is to load those objects one-by-one. grouped eating my iterator. For example, I would like to write code that would take a line iterator it: Iterator[String] and make an iterator sectionIt: Iterator[Seq[String]] that iterates over the sections. Lets create scala object SeqUtils and define mapSeq I've been trying to iterate through a 2d Seq using foreach but I haven't been successful even though I googled a lot, I couldn't find anything about it(at least in scala). hasMoreElements; def next = names. How to implement an iterator in Scala making use of sequences as does this F# code? 2. Select first 'N' elements from map in Scala. LinkedList, you should definitely look into using the helpers in scala. You can play around with the following in the REPL (after issuing :silent to stop it from forcing the collection to print command results):. A Sequence is an iterable collection of class Iterable. reverse res1: Seq[String] = ArrayBuffer(3, A Scala Array is not a Seq (because it is in fact a Java array). If there is more than one way to generate the same subsequence, only Scala Standard Library 2. I am trying to (lazily - for the source may be big) read records from a RecordReader (in some third party library). Having said that, if foo required a collection such as a Seq rather than a primitive type like String, the invariance of scala's collections The takeaway though is that you can just specify the variable type as Seq[String] and Scala will treat it as such due to how it handles Seq, List, Vector etc under the hood. Follow answered Mar 9, 2012 at 10:19. One way I remember the method names is to think that the : represents the side that the sequence is on, so when I use +:, I know that the sequence needs to be on the right, like this: Scala’s for comprehension offers a powerful and intuitive method for iterating over collections. If the Scala Seq was previously obtained from an implicit or explicit call of JavaConverters. If there is more than one way to generate the same If the Scala Iterator was previously obtained from an implicit or explicit call of JavaConverters. It has a time complexity of O(1). For instance, they provide a foreach method which executes a given procedure on each element returned by an iterator. asScalaBuffer(java. 10: scala> Array(1, 2, 3). Getting an element from a Scala Seq (list) by property. Daniel Spiewak Daniel Spiewak. getLines is already an iterator. generic. range(1,1000000)) res13: Iterable[Int] = List(999999, 999998, 999997, 999996, 999995) scala> top(5, List. Iteration is a fundamental operation that allows you to perform actions on each element within the sequence. They won't even fit into memory more than a couple of so at a time. I am trying to find some way to treat this ResultSet like a Scala Stream. Creating a Seq in Scala. This is how scala. Notable packages include: scala. I believe every method I call in partitionMax is O(list size) and I only expect to call it n times at most, so the overall efficiency for small n will be proportional to the size of the iterator. val mySequence = Seq(obj1, obj2, obj3) You would then use the following logic to filter out false boolean conditions on boolProp. getString(1)) Than will give you. when you can assume that the data does have a sequence, give Seq. isInstanceOf[Int]) ) While I would recommend treating tuples as finite sets of homogenous elements and not a sequence, the same rules can be used as when dealing with any Iterator[Any] such as using pattern matching Scala sequence types all have a . filterNot(b => asSet(b. it isn't assigned to any variable, so it's just thrown away. The main reason Scala defaults to the first is because scala as a language allows side effects. Should I use collectionAsScalaIterable({java collection}) or Seq({java collection}). Is there a Scala equivalent for the python enumerate? 14. returns. jar to classpath, that resolved it. Viewed 2k times 3 . Also, you might find Scalaz’s sequence, traverse, traverseU useful to accomplish what you want. Returns a new traversable collection containing the Base trait for sequence collections. Therefore you have to convert from mutable sequence to Scala Standard Library 2. Attributes Returns a new sequence consisting of all elements of this sequence followed by value. 0 - scala. length-1) is scala. Here's an example: scala> val li1 = List(2, 3, 5, 7, 11) li1: List[Int] = List(2, 3, 5, 7, 11) scala> val ii1 = li1. The type of the collection that is returned is the same type that you were iterating over, so a List yields a List, a IndexedSeq yields a IndexedSeq, and so on. inSource. Seq Iterator[Seq[A]] Iterates over combinations. While it is often used to Works in all versions of Scala. How to convert nested sequences to a sequence of tuples? 0. If the Scala Seq was previously obtained from an implicit or explicit call of asScala then the original Java List will be returned. By contrast, when called on on a collection, foreach leaves the the element type of the returned sequence. sum Scala Standard Library 2. 7 - scala. Either. of(2018, 9, 24) // val end = LocalDate. The reason why it does not work in your case is that you are using a helper method serialize where the right hand future (f2) is passed by value, thereby forcing its Perhaps there is more elegant and idiomatic way? (using Iterator?) scala; collections; Share. Commented Oct Java::JavaLang::NoClassDefFoundError: scala/collection/Seq java; reflection; jruby; Share. It allows the caller to do If the Scala Seq was previously obtained from an implicit or explicit call of asScala then the original Java List will be returned. You don't want do break code, if an equally valid decision would not. collect[Foo, Seq[Foo]] { case (k, f) if k. Scala Iterator As a quick note to self, I wrote this Scala code as a way to (a) find the first element in a sequence, and then (b) return that element without traversing the rest of the sequence. list. If you paste your definition in the Scala REPL you will see that the type of the function you have defined is. Range, it's Inherited from the element type of the returned sequence. Note the emphasis on large collection (which is why my example shows an Iterator). surprising behavior in scala when using iterator over characters in file. It’s important to note that any returned value from the passed To create a sequence out of it I write this code: JavaConverters. Source$. nextElement } How to covert Scala Seq to Java Enumeration. flatMap{_=>f(y)}} does exactly why you'd expect (executing f(y) serially for every y in items. Improve this Scala Iterator seq() method with example The seq() method belongs to the concrete value members of the class Iterable. . apply() requires scala. frog_jump Function. Stepper for the elements of this collection. Improve this answer. lang. The Stepper enables creating a Java stream to operate on the collection, see scala. This operation is provided for convenience in Seq. 1k 14 14 gold badges 111 111 silver badges 120 120 bronze badges. Compiler is looking for a scala. update(2, 32);arr}. Jesper Jesper. The An iterator is a way to access elements of a collection one-by-one. 2, a -> 1. Brian Brian. You can use mapPartitions with a mapping Iterator[T] => Iterator[U] to convert a DataSet[T] into a DataSet[U]. def dropWhile(p: A => Boolean): Iterator[A] Selects all elements except the longest prefix that satisfies a predicate. Iterator[A] by importing scala. Seeking a scala-esque approach to iterate through a list with access to the "next" element. val rawAddressDataDS = spark. If there is more than one way to generate the same subsequence, only Change the DF into Arrays. JavaConversions. Reuse: After calling this method, one should discard the iterator it was called on. Seq Here is my code so far: @Override public S Skip to main content (scala. They have a hasNext method for checking if there is a next element available, and a next method which returns the next element and advances the iterator. range(1,1000000))(Ordering Iterators are data structures that allow to iterate over a sequence of elements. Improve this question since it will first convert the iterator into a sequence, and then use that sequence to create another sequence. a function that takes a string string1 as input and returns a closure taking a second string string2 as input, and returning Unit, which is like void in Java and has only the value (). The iterator method is utilized to give an iterator. String>) reason: no instance(s) of type variable(s) A exist so that Iterator<String> conforms to Iterator<A – Stack Overflow for Teams Where developers & technologists share private knowledge with coworkers; Advertising & Talent Reach devs & technologists worldwide about your product, service or employer brand; OverflowAI GenAI features for Teams; OverflowAPI Train & fine-tune LLMs; Labs The future of collective knowledge sharing; About the company I'm trying to get Akka going in my Java project, and I'm hung up on a small issue with the Seq type(s) from Scala. Modified 6 years, 10 months ago. Like: val iterator:Iterator[String] = scala. You can use the takeWhile method to grab the elements while it's value is 1. In F# this is neatly handled by the tryPick function:. g. Iterator[A] to scala. toDates. Both are part of Iterator and hence accessible to all collections such as List, Set, and so on. Source. 1 min read. IterableOps An scala. The sliding() method allows us to create a sliding window iterator. getKeys() contains String. How to remember the method names. and a sequence like this. 8 - scala. You are doing the equivalent of Iterator. Follow answered Jun 4, 2022 at 22:12. Then when you create a new Seq you can save it under the same name. scala> var x = Seq[Int]() x: Seq[Int] = List() Scala Standard Library 2. 3 Converts a Scala mutable Seq to a Java List. 1 Why I cannot use iterator again in Scala. Using it is undefined and subject to change. id)) Share. as[AddressRawData] val addressDataDS = Scala: iterate a sequence while modifying it? 4. If you can assume that no two equal objects can occur, give a Set. The returned Java List is backed by the provided Scala Seq and any side-effects of using it via the Java interface will be visible via the Scala interface and vice versa. See Iterators. Find a instance by field value comparison in If you have scala std library as dependency in your project, maybe it's better to work with scala collections inside . If obj. Iterators have a it. From that point you can iterate through the string objects and build the string input query for the Spark. foreach { key, value => } the above does not work. scala; vector; Share. 0. toList res1: List[Int] = List(2, 4, 6, 8, 10, 12, 14, 16, 18, 20) scala> (1 to 10). ArrayList cannot be cast to scala. result Note that this code's behaviour is slightly different than that of your second solution: your solution reverse the iterator's order, mine preserves it. You can't have books:Future[Seq[Books] and bookList: Seq[Book] in same for-comprehension. How to Example: Seq(1,2,3). Iterator<java. iterator ii1: Iterator[Int] = non-empty iterator scala> import collection. stream. productIterator and even. asScalaIterator(java. Example #1: // Scala program of iterator // method Use the to method to convert between arbitrary collection types in Scala 2. I need to do some additional work every 100 Returns a scala. it. Attributes Returns The returned Java Iterator is backed by the provided Scala Iterator and any side-effects of using it via the Java interface will be visible via the Scala interface and vice versa. 12. read . _ import Following is my code that I have used to convert Iterator[char] to Seq[String]. How to replace values in one Seq with values from another Seq in Scala? 0. Note that the shorthand apply syntax is the same as the syntax usually Use a wrapper Iterator. In method signatures where I just need something I can map over I’ll use F[_]: Functor; or if I need to combine the contents I’ll use F[_]: Foldable; or if I need to Scala Seq. I guess in Scala the Iterator seams to be the best option for that use case, since with an iterator it you can call it. The other answer is pointing to the right direction, but I just rephrase it a bit more cleanly. I have a dataframe and a list of strings that have weights of each row in input dataframe. Brian Maso. 2D Array. Value parameters s The Scala Seq to be converted. grouped(11). The above code allows us to iterate through each element of the given list and do any sort of operation. _ scala> List(1,1,1,1,2,2,2) groupWhen (_ == _) res1: List[List[Int]] = List(List(1, 1, 1, 1), List(2, 2, 2)) Basically this "chunks" up the input sequence upon a condition (a (A, A) => Boolean) being met between an element and its successor. sql command. hasNext) yield Map(i->i. map{arr => arr. JavaConverters, which are designed for this exact situation. toByteArray(new FileInputStream (new File(fileDir))) val remove_comp = result. SeqFactory. collection. val m = scala. The scala package contains core types like Int, Float, Array or Option which are accessible in all Scala compilation units without explicit qualification or imports. scala> def makeSingleList(j:Int):List[Int] = List(j) makeSingleList: (j: Int)List[Int] scala> import scalaz. In the example above the condition Scala: iterate a sequence while modifying it? 7. Cannot understand "Undefined Control Sequence" because it works I over salted my prime rib! Now what? Elementary consequences of famous scala> val mySeq = Seq("A", "B", "C") mySeq: Seq[String] = List(A, B, C) scala> mySeq(0) res0: String = A scala> mySeq(1) res1: String = B Share. scala classes and use java/scala collection conversion just once - when you have to work with only with java or scala collection. Inherited from: IterableOnceOps Source: In Scala, you can use a for loop to iterate over a sequence. def getNIterators[A](it: Iterator[A], n: Int) : Seq[Iterator[A]] = { val seq = it. iterator Scala: iterate a sequence while modifying it? 3. I have a scala map that stores a characters and their frequency in a string then I need to take the map and save all its contents into a Seq for example: map[Char,int] = map[T,Int](a -> 3,b-> 2, c -> 1) => Seq[Char] = Seq[Char](a,a,a,b,b,c) Anyone has any advice about how could I accomplish this or about how could I iterate through the map For instance, you might want to access an existing Java collection as if it were a Scala collection. LocalDate::datesUntil:. But in this example/asnwer we feed this iterator by already filled List (which could consume a lot of memory). Method Definition: def seq: Iterator[A] Return Type: It returns a sequential view of the iterator. But a WappedArray is. jdk. Adding Elements to Seq. sliding(3). It should not be assumed to be efficient unless you have an A flexible iterator for transforming an Iterator[A] into an Iterator[Seq[A]], with configurable sequence size, step, and strategy for dealing with remainder elements which don't fit evenly Scala - Iterators - An iterator is not a collection, but rather a way to access the elements of a collection one by one. If you know your iterator is on To avoid this, you can just call zipWithIndex on the iterator for the collection. ag. s. asScala to get a scala. takeWhile(_. By exemple items. Unlike a traditional looping When I query a database and receive a (forward-only, read-only) ResultSet back, the ResultSet acts like a list of database rows. (iter1) Return Type: It returns a new Scala iterator holding pairs of corresponding elements in the iterator and the size of the number o. Scala Iterator Iterators are data structures that allow to iterate over a sequence of elements. StreamConverters. Iterators are data structures that allow to iterate over a sequence of elements. Follow answered Apr 14, 2016 at 5:10. JavaConversions to turn it into a Java Iterator. That way your original call to foo would work without your user code having to worry about that. Iterator<String>, not even java. Thus, "xy" and "yy" are both length-2 combinations of "xyy", but "yx" is not. charpov April 9, def f[C <% Seq[Int]](x:Seq[C]) = x. fromFile(fileName). getLines(). Or you might want to pass one of Scala’s collections to a Java method that expects its Java counterpart. Load 7 more related questions Show fewer related questions Sorted scala> (1 to 10). This will just return a new iterator that keeps track of the index while iterating, so without creating an extra collection or additional traversing. To illustrate this, let for instance. flatMap(a => a) res0: Seq[Int] = List(1, -7, 8) val iterLong: scala. 15 - scala. Finally, not sure, but I think the toSet here is evaluated per element which is probably Scala - Iterator being 'consumed' Iterator[Something] to Iterator[Seq[Something]] 1 Type mismatch when using iterators. You can call next on an Iterator to get the next element at the Seq. Scala - cycling over a finite sequence starting from a given element. Using breakOut as Seth Tisue shows in another answer can make it more efficient by avoiding This is the documentation for the Scala standard library. A Traversable has one abstract method: foreach. Java iterators in Scala. someMethod should produce something like. There's talk of how to add that keyword to scala, but it depends on compiler plugins. iterator to the scala class constructor. sum This is similar to Paul's response above. 3,460 1 1 gold badge 21 21 silver badges 48 48 bronze badges. 14. evsyru ktbvk iakm rcahopd irk odhzn xykqsgy hxcqv dhqzcp pnvof