Joseph forgot to add the value in his example with withDefault
.
Here is the code I ended up using:
Map map = [:].withDefault { key -> return [] }
listOfObjects.each { map.get(it.myKey).add(it.myValue) }
def map = [:]
map["stringKey"] = [1, 2, 3, 4]
map["anotherKey"] = [55, 66, 77]
assert map["anotherKey"] == [55, 66, 77]
you don't need to declare Map groovy internally recognizes it
def personDetails = [firstName:'John', lastName:'Doe', fullName:'John Doe']
// print the values..
println "First Name: ${personDetails.firstName}"
println "Last Name: ${personDetails.lastName}"
One additional small piece that is helpful when dealing with maps/list as the value in a map is the withDefault(Closure)
method on maps in groovy. Instead of doing the following code:
Map m = [:]
for(object in listOfObjects)
{
if(m.containsKey(object.myKey))
{
m.get(object.myKey).add(object.myValue)
}
else
{
m.put(object.myKey, [object.myValue]
}
}
You can do the following:
Map m = [:].withDefault{key -> return []}
for(object in listOfObjects)
{
List valueList = m.get(object.myKey)
m.put(object.myKey, valueList)
}
With default can be used for other things as well, but I find this the most common use case for me.
API: http://www.groovy-lang.org/gdk.html
Map -> withDefault(Closure)
Source: Stackoverflow.com