List<String> strs = Lists.newArrayList("Inky", "Blinky", "Pinky", "Pinky", "Clyde");
ImmutableListMultimap<Integer, String> idx = Multimaps.index(strs, new Function<String, Integer>() {
	public Integer apply(String input) {
		return input.length();
	}
});
System.out.println(idx);
System.out.println(idx.get(5));
System.out.println(idx.get(5).size());

{4=[Inky], 6=[Blinky], 5=[Pinky, Pinky, Clyde]}
[Pinky, Pinky, Clyde]
3