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except that applyOrElse method can be implemented more efficiently. For all partial function literals the compiler generates an applyOrElse implementation which avoids double evaluation …

Now Map also has a mapValues method, which seems like an attractive ... You can see this in the source code of the Scala standard library: ...

4 Answers. Sorted by: 71. mapValues is only applicable for PairRDDs, meaning RDDs of the form RDD [ (A, B)]. In that case, mapValues operates on the value only (the …

Lookup operations apply, get, getOrElse, contains, and isDefinedAt. These turn maps into partial functions from keys to values. The fundamental lookup method for a map is: def get (key): …

Builds a new iterable collection by applying a function to all elements of this iterable collection and using the elements of the resulting collections. Builds ...

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Builds a new collection by applying a partial function to all elements of this map on which the function is defined. def collectFirst [B] (pf: PartialFunction [ (K, W), B]): Option [B] Finds the first element of the collection for which the given partial function is defined, and applies the partial function to it.

Learn all about Scala's Map data type. ... If we want to transform only values, we can use the mapValues method and pass a mapping function ...

1) As pointed out by @Kigyo, the right answer, given that there are no duplicate a s, wouldn't use groupBy: val m: Map [Int,Foo] = data.map (e => e.a -> e) (breakOut) Using …

Scala’s Predef object offers an implicit conversion that lets you write key -> value as an alternate syntax for the pair (key, value). For instance Map("x" -> 24, "y" -> 25, "z" -> 26) means exactly the same as Map(("x", 24), ("y", 25), ("z", 26)), but reads better. The fundamental operations on maps are similar to those on sets.

mapValues creates a Map that is NOT serializable, without any indication that it's just a view (the type is Map[_, _] , but just try to send one ...

Sometimes you have a PairRDD (Key, Value) where the value is a tuple. What if you want to add the values in the tuple for each key.

Scala's MapLike trait has a method mapValues [C] (f: (B) ⇒ C): Map[A, C] But I sometimes want a different type: mapKeysAndValues [C] (f: (A, B) ⇒ C): Map[A, C] Is there a …

mapValues creates a Map with the same keys from this Map but transforming each key's value using the function f . English · Español · 日本語 · Português ...

Let's say we have a Map[A,B].For clarification: I'm always referring to an immutable Map.. mapValues takes a function B => C, where C is the new type for the values.. transform takes a function (A, B) => C, where this C is also the type for the values.. So both will …

Keep in mind that the MappedValues implementation evaluates the function on every access -- different from a Scala lazy val that evaluates only once. You might be seeing …

Copy elements to an array, returning the number of elements written. Fills the given array xs starting at index start with at most len elements of this collection.. Copying will stop once either …

to scala-user ... to John, scala-user. You can add the check in your mapValues. If the check fails, ... scala> val m1 = Map[String, Int]("x"->0, "y"->20).

Aug 29, 2013 · 2. mapValues is just like map but for values :) Map may be viewed as a list of pairs (key, value). So, when you just execute map - you transform a tuple (key, value), but in mapValues you transform only a value. mapValues (f) is equivalent of map { case (k, v) => k -> f (v) }. – dmitry.

Builds a new iterable collection by applying a partial function to all elements of this iterable collection on which the function is defined. Type parameters.

Map.scala def collectFirst [ B ]( pf : PartialFunction [( K , W ), B ]): Option [ B ] Finds the first element of the collection for which the given partial function is defined, and applies the partial function to it.

Scala mapValues function. Graphical representation of the Scala's mapValues function. Visual Scala Reference. mapValues. traitMap[K, V]{defmapValues[W](f:(V)=>W):Map[K, W]} …

Sep 3, 2014 · Since mapValues is just a view, every instance contains the real Map - which could be another result of mapValues. Imagine you have an actor with some state, and every mutation of the state sets the new state to be a mapValues on the previous state...in the end you have deeply nested maps with a copy of each previous state of the actor (and, yes, both of these are from experience).