Sort Map of String,List<String> by Value List size-CodePudding

I need to sort the hashmap based on value List size and its' not working. I've written my custom comparator. For example hashmap is as follow:

Test1-a,b
Test2-c,d,e
Test3-f
Test4-d,g,h,i
Test5-p,b

After sorting it should look like this:

Test3-f
Test1-a,b
Test5-p,b
Test2-c,d,e
Test4-d,g,h,i

Sorting the keys based on value list size in ascending order. I wrote this code and it's not working:

List<Map.Entry<String,List<String>>> list =
        new ArrayList<>(map.entrySet());

Collections.sort( list, new Comparator<Map.Entry<String,List<String>>>() {
    public int compare( Map.Entry<String,List<String>> o1,
                        Map.Entry<String,List<String>> o2) {
        return o1.getValue().size().compareTo(o2.getValue().size() );
    }
});

CodePudding user response：

Your code is not compilabe, because List.size() returns an (unboxed) int .. we cannot invoke "methods" on that.

Instead try:

Collections.sort( 
  list,
  // when java >= 8, we can save all the "decoration" (anonymous class), and "lambda" instead:
  (o1,o2) -> Integer.compare(o1.getValue().size(), o2.getValue().size())
);

Javadoc (Integer.compare(int x, int y)): https://docs.oracle.com/en/java/javase/19/docs/api/java.base/java/lang/Integer.html#compare(int,int)

Its implementation looks as simple as:

public static int compare(int x, int y) {
  return (x < y) ? -1 : ((x == y) ? 0 : 1);
}

CodePudding user response：

Putting the above answer together with your code, you could do

        List<Map.Entry<String,List<String>>> list = 
        m.entrySet()
            .stream()
            .sorted((e1, e2) -> Integer.compare(e1.getValue().size(), e2.getValue().size()))
            .collect(Collectors.toList());
        System.out.println(list);