How to retrieve a key from the Map<String,List<String>> based on its value (an element of a list)?

Question

I have a map looking like this:

def myMap = [
 'Key1': ['nameOfApp', 'nameOfApp2', 'nameOfApp3'],
 'Key5': ['nameOfApp4'],
 'Key2': ['nameOfApp5'],
 'Key3': ['xxx', 'yyy'],
 'Key4': ['aaa', 'vvv']
]

How can I find the KEY by providing a VALUE (which is a simple String value) ? I've tried lots of things but I'm blocked with the fact that values are lists...

As an example, if I provide nameOfApp2, I expect to get the key Key1. What's the easiest way to achieve it with Groovy?

• Strelok: Boggles the mind why anyone would design a map and look up something by "value" why don’t you invert the map?
• Tony Lecointre: The fact is that I can't update this part of the code because it's not on my scope. I'm using this map via Jenkins External Library.

Answer 1

You can use find method with a predicate like expectedValue in it.value. Check the following example:

def myMap = [
 'Key1': ['nameOfApp', 'nameOfApp2', 'nameOfApp3'],
 'Key5': ['nameOfApp4'],
 'Key2': ['nameOfApp5'],
 'Key3': ['xxx', 'yyy'],
 'Key4': ['aaa', 'vvv']
]
def expectedValue = 'nameOfApp2'
def key = myMap.find { expectedValue in it.value }?.key
assert key == 'Key1'

The variable it inside the predicate closure represents each Map.Entry<String. List<String>> from the input map, so you can check if the expected value is a part of it.value list. And the last part uses ?.key null safe operator to get the value of the key, just in case expected value is not present in any list.

• Tony Lecointre: Thanks a lot, it works well. I was really close but my knowledges about Groovy are low. Thanks again :)