CODEWITHSUNDEEP
scaladictionarytuples
More Than Five
More Than Five

Reputation: 10429

Extract second tuple element in list of tuples

I have a Map where each value is a list of Tuples such as:

List(('a',1), ('b', 4), ('c', 3)....)

what is the most scala-thonic way to change each value is still a LIst but is only the second element of each Tuple

List(1,4,3)

I have tried

myMap.mapValues(x => x._2)

And I get 

error: value _2 is not a member of List[(Char, Integer)]

any tips?

Upvotes: 12

Views: 21122

Answers (4)

henko
henko

Reputation: 763

Another way is using unzip which turns a list of tuples into a tuple of lists. It is especially useful if you actually want both values from the tuples.

val list = List(('a',1), ('b', 4), ('c', 3))

val (letters, numbers) = list.unzip
// letters: List[Char] = List(a, b, c)
// numbers: List[Int] = List(1, 4, 3)

Upvotes: 0

Chengye Zhao
Chengye Zhao

Reputation: 166

Would that work for you?

val a = List(('a',1), ('b', 4), ('c', 3))
a.map(_._2)

Upvotes: 8

trenobus
trenobus

Reputation: 236

Note that mapValues() returns a view on myMap. If myMap is mutable and is modified, the corresponding changes will appear in the map returned by mapValues. If you really don't want your original map after the transformation, you may want to use map() instead of mapValues():

myMap.map(pair => (pair._1, pair._2.map(_._2)))

Upvotes: 2

cmbaxter
cmbaxter

Reputation: 35463

Try this:

    myMap.mapValues(_.map(_._2))

The value passed to mapValues is a List[(Char,Integer)], so you have to further map that to the second element of the tuple.

Upvotes: 10

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