Question

I have a Map<X, Y> and List<X>, I would like to extract the values from Map<X, Y> by providing the List<X>, which will result in List<Y>. One way to do this is

List<X> keys = getKeys();  
Map<X, Y> map = getMap();  
List<Y> values = Lists.newArrayListWithCapacity(keys.size());  
for(X x : keys){  
   values.add(map.get(x));  
}

Now again I need to remove nulls in values (List<Y>) by using Predicate or something. Any better way to do this?
Is there any good reason why this method isn’t there in google collections library?

Answer 1

Something like this:

List<Y> values = Lists.newArrayList(
    Iterables.filter(
        Lists.transform(getKeys(), Functions.forMap(getMap(), null), 
        Predicates.notNull()));