user971956 user971956 - 3 months ago 10
Groovy Question

Add two maps in Groovy while summing up values for common keys

I have two maps in Groovy

[a: 1, b: 2]
and
[b:1, c:3]
and would like to create from them a third map
[a: 1, b: 3, c: 3]
. Is there a Groovy command that does that?

Edit: Notice that the values in the third map, are a sum of the values from the first two maps, if the keys are identical.

Thanks

Answer

Yet another solution would be:

def m1 = [ a:1, b:2 ]
def m2 = [ b:1, c:3 ]

def newMap = [m1,m2]*.keySet().flatten().unique().collectEntries {
  [ (it): [m1,m2]*.get( it ).findAll().sum() ]
}

Taking epidemian's answer as inspiriation, you can also write a method to handle multiple maps

def m1 = [a: 1, b: 2]
def m2 = [b: 1, c: 3]

def combine( Map... m ) {
  m.collectMany { it.entrySet() }.inject( [:] ) { result, e ->
    result << [ (e.key):e.value + ( result[ e.key ] ?: 0 ) ]
  }
}

def newMap = combine( m1, m2 )
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