Java 8 sort Map<String, List<Double>> - sorting

Question

How to sort a Map > according to average of all the values in the list using Java8 streams?
I couldn't figure out how to collect the sorted map to another instance of map. Thanks for the help in advance.
Here is the code that I tried
Map<String,List<Double>> map = new HashMap<String,List<Double>>();
LinkedList<Double> list1 = new LinkedList<Double>(Arrays.asList(12.5,45.67));
map.put("1",list1);
LinkedList<Double> list2 = new LinkedList<Double>(Arrays.asList(13.5,49.67));
map.put("2", list2);
LinkedList<Double> list3 = new LinkedList<Double>(Arrays.asList(10.5,9.67));
map.put("3", list3);
LinkedList<Double> list4 = new LinkedList<Double>(Arrays.asList(1.5,40.67));
map.put("4", list4);
map.entrySet().stream().sorted(new Comparator<Map.Entry<String, List<Double>>>() {
#Override
public int compare(Entry<String, List<Double>> arg0, Entry<String, List<Double>> arg1) {
return (int)(((LinkedList<Double>)arg1.getValue()).stream().mapToDouble(Double::doubleValue).sum() - ((LinkedList<Double>)arg0.getValue()).stream().mapToDouble(Double::doubleValue).sum());
}
});
System.out.println(map);
The output I get is still the same Map with out sorting. The expected output here is a map with the entries in this order
<"2", list2>
<"1", list1>
<"4", list4>
<"3", list3>
Edit:
Here is the solution I got to
Map<String,List<Double>> map = new HashMap<String,List<Double>>();
LinkedList<Double> list1 = new LinkedList<Double>(Arrays.asList(12.5,45.67));
map.put("1",list1);
LinkedList<Double> list2 = new LinkedList<Double>(Arrays.asList(13.5,49.67));
map.put("2", list2);
LinkedList<Double> list3 = new LinkedList<Double>(Arrays.asList(10.5,9.67));
map.put("3", list3);
LinkedList<Double> list4 = new LinkedList<Double>(Arrays.asList(1.5,40.67));
map.put("4", list4);
LinkedHashMap<String,List<Double>> orderedMap = new LinkedHashMap<String,List<Double>>();
Iterator<Entry<String, List<Double>>> iterator = map.entrySet().stream().sorted(new Comparator<Map.Entry<String, List<Double>>>() {
#Override
public int compare(Entry<String, List<Double>> arg0,
Entry<String, List<Double>> arg1) {
return (int)((((LinkedList<Double>) arg1.getValue()).stream().mapToDouble(Double::doubleValue).sum() - ((LinkedList<Double>)arg0.getValue()).stream().mapToDouble(Double::doubleValue).sum()));
}
}).iterator();
while(iterator.hasNext()){
Entry<String, List<Double>> next = iterator.next();
orderedMap.put(next.getKey(), next.getValue());
}
System.out.println(orderedMap);
I am not happy with this solution. Is there a precise and better way of doing this?

Answer 1

Your comparator doesn’t do the job you want, or at least not always. It works only if all the lists have the same size because you are comparing the sum not the average values for each list. I created a new Comparator based on lists average values and simplified the code. Below is my code:
Comparator<Map.Entry<String,List<Double>>> byAverange =
(Entry<String,List<Double>> o1, Entry<String,List<Double>> o2)->
{
return ((Double)o2.getValue().stream().mapToDouble(a -> a).average().getAsDouble())
.compareTo(
o1.getValue().stream().mapToDouble(a -> a).average().getAsDouble());
};
LinkedHashMap<String, List<Double>> ordered = new LinkedHashMap<>();
map.entrySet().stream().sorted(byAverange).forEach(entry -> ordered.put(entry.getKey(), entry.getValue()));
System.out.println(ordered);
output:
{2=[13.5, 49.67], 1=[12.5, 45.67], 4=[1.5, 40.67], 3=[10.5, 9.67]}
hope this can help.