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  1. /* package whatever; // don't place package name! */
  2.  
  3. import java.util.*;
  4. import java.lang.*;
  5. import java.io.*;
  6. import java.util.stream.Collectors;
  7.  
  8. /* Name of the class has to be "Main" only if the class is public. */
  9. class Ideone
  10. {
  11. 	public static class Obj {
  12. 		private int value;
  13. 		private String category;
  14.  
  15. 		public Obj(int value, String category) {
  16. 			this.value = value;
  17. 			this.category = category;
  18. 		}
  19.  
  20. 		public int getValue() { return value; }
  21. 		public void setValue(int value) { this.value = value; }
  22.  
  23. 		public String getCategory() { return category; };
  24. 		public void setCategory(String category) {this.category = category; };
  25.  
  26.  
  27. 		@Override
  28. 		public String toString() {
  29. 			return category + ":" + value;
  30. 		}
  31. 	}
  32.  
  33. 	public static void main (String[] args) throws java.lang.Exception
  34. 	{
  35. 		List<Obj> list = new ArrayList<>();
  36. 		list.add(new Obj(500, "GROCERY"));
  37. 		list.add(new Obj(300, "GROCERY"));
  38. 		list.add(new Obj(100, "FUEL"));
  39. 		list.add(new Obj(300, "SMALL APPLIANCE REPAIR"));
  40. 		list.add(new Obj(200, "FUEL"));
  41.  
  42. 		List<Obj> values = list.stream().collect(
  43.         Collectors.groupingBy(Obj::getCategory, Collectors.reducing((a, b) -> new Obj(a.getValue() + b.getValue(), a.getCategory())))
  44.     ).values().stream().map(Optional::get).collect(Collectors.toList());
  45.  
  46. 	List<Obj> values2 = list.stream().sorted((o1, o2) -> o1.getCategory().compareTo(o2.getCategory()))
  47.         .collect(LinkedList<Obj>::new, (ll, obj) -> {
  48.               Obj last = null;
  49.               if(!ll.isEmpty()) {
  50.               	last = ll.getLast();
  51.               }
  52.  
  53.               if (last == null || !last.getCategory().equals(obj.getCategory())) {
  54.                 ll.add(new Obj(obj.getValue(), obj.getCategory())); //deep copy here
  55.               } else {
  56.                 last.setValue(last.getValue() + obj.getValue());
  57.               }
  58.             },
  59.             (list1, list2) -> {
  60.               throw new RuntimeException("parallel evaluation not supported");
  61.             });
  62.  
  63.  
  64. 		System.out.println(values);
  65. 		System.out.println(values2);
  66. 		// your code goes here
  67. 	}
  68. }
Success #stdin #stdout 0.23s 320960KB
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[SMALL APPLIANCE REPAIR:300, FUEL:300, GROCERY:800]
[FUEL:300, GROCERY:800, SMALL APPLIANCE REPAIR:300]
https://ideone.com/p3bKV8
language:
Java (HotSpot 12)
created:
9 years ago
visibility:
public

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