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If the list was List (1,2,3,4) then the filter method would return a new list: List (3,4). For instance, for list.filter (a > a > 2), the list will be filtered down to only keep the elements that are > 2 (greater than 2). Filtering a Map Problem You want to filter the elements contained in a map, either by directly modifying a mutable map, or by applying a filtering algorithm on an immutable map to create a new map. If you are asking because this is a performance bottleneck, then the answer is usually to write a tail-recursive function or use the old-style while loop method. Datasets can also be created through transformations available on existing Datasets. The filter method allows you to keep the elements of the list that return true for the test (Also called a lambda function). Filtering a Map - Scala Cookbook Book 11.21. The advantage of this approach is that it's really easy to read and, since there are no intermediate collections, it's reasonably efficient. You then map first and filter afterwards and then map again if needed: xs.iterator.map(x => x*x).filter(_ > N).map(_.toString) : def filter (p: ( (A, B))> Boolean): Map A, B : It returns a new map consisting all the elements of the map which satisfies the given predicate. Notable packages include: llection and its sub-packages contain Scalas collections framework.

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 Values Scala String Interpolation Scala Methods Scala Method with Arguments Scala List Sum Method Scala Option Scala difference between val, lazy val and def Scala Map for List Scala Class new Scala Comparators Scala List Filter Method Scala Call-by-name Parameters Scala Case Class Scala objects Scala visibility Scala companion objects Scala apply Scala Option map Scala List Flatten. This doesn't exactly avoid two traversals, but it does avoid creation of a full-sized intermediate collection. This is the documentation for the Scala standard library. The typical approach is to use an iterator (if possible) or view (if iterator won't work).