Finding the key in a map, given the value

Question

Hi I have a map like this :

[this:0, is:1, a:2, file:3, anotherkey:4, aa:5]

I wish I could find the key\'s given the value

Answer 1

I don't know if there's a direct method to get a key for a given value, but using Map#find to get a map entry and then get its value should be enough:

def keyForValue(map, value) {
    map.find { it.value == value }?.key
}

def map = [a: 1, b: 2, c: 3]
assert keyForValue(map, 2) == 'b'
assert keyForValue(map, 42) == null

In general, maps don't need to have an order relation between their entries, but the default implementation for Groovy's literal maps is LinkedHashMap, which is ordered, so the keyForValue will always yield the first key for a value when using those maps.