Question

For example if the map is equal to:

z = ['x':1, 'y':2]

For f(2) I would like it to become:

[x':2, 'y':4]

I know it could be done using a .each loop, question is whether there is a simpler way.

Thank you

Answer 1

There’s the collectEntries function, which is applied to all keys and values in a Map, and returns a new Map with the updated values:

def z = [x:1, y:2]
z = z.collectEntries{ key, value -> [(key): value*2] }
assert z == [x:2, y:4]

A couple of notes here:

• First, you don’t need to quote string keys in map literals, meaning ['z':1] is the same as [z:1], but the latter is groovier and more legible
• Second, the return value of the collectEntries closure must be a map, so be careful there
• Third, when providing dynamic keys in a map, you need to wrap them in parentheses, so you need to use (key), not just key
• Fourth, you need to assign the result of the method, it doesn’t act in-place.

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However, it’s almost certainly just be cleaner to use each() with the single-argument closure, like so:

def z = [x:1, y:2]
z.each{ it.value = it.value*2 }
assert z == [x:2, y:4]

There’s less gotchyas this way, and it modifies the map in-place, so you don’t have to reassign the variable.