Remove key/value from map while iterating

Question

I'm creating a map like this:

def myMap = [:]

The map is basically an object for a key and an int for a value. When I iterate over the map, I decret the value, and if it's 0, I remove it. I already tried myMap.remove(), but I get a ConcurrentModificationError - which is fair enough. So I move on to using it.remove(), which is giving me weird results.

Basically, my code is this:

myMap.each {
    it.value--;

    if( it.value <= 0 )
        it.remove();
}

Simple enough. My problem is, if I print myMap.size() before and after the remove, they're the same. If I call myMap.containsKey( key ), it gives me true, the key is still in there.

But, if I print out the map like this:

myMap.each { System.out.println( "$it.key: $it.value" ); }

I get nothing, and calling myMap.keySet() and myMap.values() return empty.

Anyone know what's going on?

Answer 1

This should be a bit more efficient than Tim's answer (because you only need to iterate over the map once). Unfortunately, it is also pretty verbose

def map = [2:1, 3:4]
def iterator = map.entrySet().iterator()

while (iterator.hasNext()) {

  if (iterator.next().value - 1 <= 0) {
    iterator.remove()
  }
}

// test that it worked
assert map == [3:4]