'Compare HashMap Values structured as List [closed]

I have a HashMap structured like

{a=[test], b=[test, test2]}

I want to compare entry values (test, test2) with each other and if any entry has same value with another one, I need to return their keys and the equal value. I want to do this in Java.

javadata-structureshashmapcompare


Solution 1:[1]

Simply reverse the Map, use your values as grouping key for the original keys where the value repeat.

Map<KeysClass, List<ValuesClass>> original = ....
Map<ValuesClass, List<KeysClass>> keysGroupedPerValue = new HashMap<>();

for(Entry<KeysClass, List<ValuesClass> entry : original) {
   for(ValuesClass value : entry.getValue()) {
      List<KeysClass> keysHavingValue = keysGroupedPerValue.computeIfAbsent(value, val -> new ArrayList<>());
      keysHavingValues.add(entry.getKey());
   }
}

There are also more elegant solutions using the Stream and Collector APIs.

Sources

This article follows the attribution requirements of Stack Overflow and is licensed under CC BY-SA 3.0.

Source: Stack Overflow

Solution Source
Solution 1 Baptiste Beauvais

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