Guava Multimap 的每个值的总和

Question

I created a Guava Multimap ListMultimap<String,String> sampleMultimap = ArrayListMultimap.create(); And added some values which I take from a text file. Now as an output I have

{Football=[10], Basketball=[1210, 1210, 1210, 120], Tennis=[1, 10, 100, 1000]}

I would like to sum each of the sports and find the highest sum. So expected result is

Basketball: 3750

Somehow I am stuck because I cant get the each one with samleMultimap.get(x) because key values are unknown and comes form text file. Is there any way to get the expected result?

Answer 1

In the end you want Map<String, Integer> where values are sums of original multimap. You can use couple views:

• Multimap#asMap() to have Map<K, Collection<V>> view of your multimap,

• Maps#transformValues(Map, Function) - to create a view of a map where each value is transformed by a function .

   Map<String, Integer> map = Maps.transformValues(multimap.asMap(), ints -> ints.stream().mapToInt(Integer::intValue).sum());

Note that if you want to perform many operations on resulted map , read caveat in documentation and for example do ImmutableMap.copyOf(map) :

The function is applied lazily, invoked when needed. This is necessary for the returned map to be a view, but it means that the function will be applied many times for bulk operations like Map.containsValue(java.lang.Object) and Map.toString() . For this to perform well, function should be fast. To avoid lazy evaluation when the returned map doesn't need to be a view, copy the returned map into a new map of your choosing.

Answer 2

With a ListMultimap you can call asMap() to get a view as a java.util.Map , then do normal map things.

If you change sampleMultimap to be an ArrayListMultimap instead of ListMultimap , then you can call keySet() directly (skip the asMap() call) and iterate over the resulting keys.

Here's an example showing how you could get each key from a ListMultimap (even if the underlying implementation is an instance of ArrayListMultimap ), then get each associated value:

ListMultimap<String,String> sampleMultimap = ArrayListMultimap.create();
Map<String,String> mapView = sampleMultimap.asMap();
for (String key : mapView.keySet()) {
    String value = mapView.get(key);
    // do something with value
}