Simplest way to iterate through a Multiset in the order of element frequency?

Question

Consider this example which prints out some device type stats. (\"DeviceType\" is an enum with a dozenish values.)

Multiset histogram = get         


        

Answer 1

Here's a method that returns a List of entries, sorted by frequency (UPDATE: used a flag to toggle ascending / descending order and used Guava's favorite toy: the Enum Singleton Pattern, as found in Effective Java, Item 3 ):

private enum EntryComp implements Comparator>{
    DESCENDING{
        @Override
        public int compare(final Entry a, final Entry b){
            return Ints.compare(b.getCount(), a.getCount());
        }
    },
    ASCENDING{
        @Override
        public int compare(final Entry a, final Entry b){
            return Ints.compare(a.getCount(), b.getCount());
        }
    },
}

public static  List> getEntriesSortedByFrequency(
    final Multiset ms, final boolean ascending){
    final List> entryList = Lists.newArrayList(ms.entrySet());
    Collections.sort(entryList, ascending
        ? EntryComp.ASCENDING
        : EntryComp.DESCENDING);
    return entryList;
}

Test code:

final Multiset ms =
    HashMultiset.create(Arrays.asList(
        "One",
        "Two", "Two",
        "Three", "Three", "Three",
        "Four", "Four", "Four", "Four"
    ));

System.out.println("ascending:");
for(final Entry entry : getEntriesSortedByFrequency(ms, true)){
    System.out.println(MessageFormat.format("{0} ({1})",
        entry.getElement(), entry.getCount()));
}

System.out.println("descending:");
for(final Entry entry : getEntriesSortedByFrequency(ms, false)){
    System.out.println(MessageFormat.format("{0} ({1})",
        entry.getElement(), entry.getCount()));
}

Output:

ascending:
One (1)
Two (2)
Three (3)
Four (4)
descending:
Four (4)
Three (3)
Two (2)
One (1)