Collect a list of pairs into a map

Question

How can we collect a list of lists of value pairs into a map where said pairs are transformed into key:value entries in the map, as in:

a = [[1,11], [2,22], [3,33]]
b = ...?
assert b == [1:11, 2:22, 3:33]

score 5 · Accepted Answer · edited Jan 21 '16 at 14:11

5

Because collectEntries works with a pair list, you can just do

def b = a.collectEntries()

edited Jan 21 '16 at 14:11

Will

answered Jan 20 '16 at 11:50

tim_yates

score 3 · Answer 2 · answered Jan 20 '16 at 11:45

3

def b = a.collectEntries {[(it.get(0)): it.get(1)]}

answered Jan 20 '16 at 11:45

AdamSkywalker

Thanks. You know, the confusing part for me is the requirement of the pair of parentheses around the first element - or just the break down of the syntax. – Basel Shishani Jan 20 '16 at 12:01
@BaselShishani yes, they look unusual, especially for java programmers – AdamSkywalker Jan 20 '16 at 12:08
1

@BaselShishani they are needed because the keys in maps are used as literal strings. `[ it : 90 ]` creates a map with a key `"it"`, whereas `[ (it) : 90 ]` creates a map with the key being the value in the `it` var – Will Jan 20 '16 at 12:11

Will · Answer 3 · 2016-01-21T14:12:15.363

2

Use collectEntries, which turns Iterables (like Lists) into Maps:

a = [[1,11], [2,22], [3,33]]
b = a.collectEntries { [ (it.first()) : it.last() ] }
assert b == [1:11, 2:22, 3:33]

edited Jan 21 '16 at 14:12

answered Jan 20 '16 at 11:46

Will

3 Answers3