Groovy Map Minus

06 June 2017

Groovy is relatively intuitive for me: I can usually guess a method or operator and find it works as I had guessed.

Removing a key/value by the key from a Map conveniently eludes me though. I always guess that I should be able to minus a key from a Map to produce a new Map with that entry /value removed. That doesn’t work, so I needed to invent my own. I still not sure how to practically apply it everywhere though, or if it’s even worthwhile. In practice, I always end up writing the findAll inline.

@Category(Map)
class MapMinus {
    Map minus(Collection keys) {
        this.findAll { k, v -> ! (k in keys) }
    }
    Map minus(Object key) {
        this - [key]
    }
}

use (MapMinus) {
    assert [b: 2, c: 3,] == [a: 1, b: 2, c: 3,] - 'a'
    assert [b: 2, c: 3,] == [a: 1, b: 2, c: 3,] - ['a']

}


Filed Under: Code Groovy Work