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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.ArrayList;
  7. import java.util.List;
  8. import java.util.Map;
  9. import java.util.function.Function;
  10. import java.util.stream.Collectors;
  11. import java.util.stream.Stream;
  12.  
  13. /* Name of the class has to be "Main" only if the class is public. */
  14. class Ideone
  15. {
  16. 	public static void main (String[] args) throws java.lang.Exception
  17. 	{
  18. 		//--------------------- Test Data ---------------------
  19.         List<DummyObj> dataToBeAdded = new ArrayList<>(List.of(
  20.                 new DummyObj("uuid1", "abcd", "mer1", 20D),
  21.                 new DummyObj("uuid1", "pqrs", "mer1", 25D),
  22.                 new DummyObj("uuid2", "xyz", "mer1", 18D)
  23.         ));
  24.  
  25.         List<DummyObj> dataToBeSubtracted = new ArrayList<>(List.of(
  26.                 new DummyObj("uuid1", "abcd", "mer1", 5D),
  27.                 new DummyObj("uuid1", "pqrs", "mer1", 2D),
  28.                 new DummyObj("uuid3", "xyz", "mer2", 10D)
  29.         ));
  30.  
  31.         //--------------------- Original Code ---------------------
  32.         Map<String, DummyObj> dataToBeAddedMap = dataToBeAdded.stream()
  33.                 .collect(Collectors.toMap(obj -> obj.getAttr1() + obj.getAttr2() + obj.getAttr3(), item -> item));
  34.  
  35.         Map<String, DummyObj> dataToBeSubtractedMap = dataToBeSubtracted.stream()
  36.                 .collect(Collectors.toMap(obj -> obj.getAttr1() + obj.getAttr2() + obj.getAttr3(),
  37.                         item -> new DummyObj(item.getAttr1(), item.getAttr2(), item.getAttr3(), -1 * item.getAttr4())));
  38.  
  39.         Map<String, DummyObj> resultantData = Stream.of(dataToBeAddedMap, dataToBeSubtractedMap)
  40.                 .flatMap(map -> map.entrySet().stream())
  41.                 .collect(Collectors.toMap(
  42.                         Map.Entry::getKey,
  43.                         Map.Entry::getValue,
  44.                         (v1, v2) -> new DummyObj(v1.getAttr1(), v1.getAttr2(), v1.getAttr3(), v1.getAttr4() + v2.getAttr4())
  45.                 ));
  46.  
  47.         System.out.println("Output w Original Solution: ");
  48.         for (DummyObj obj: resultantData.values()){
  49.             System.out.println(obj);
  50.         }
  51.  
  52.  
  53.         //--------------------- Optimized Version ---------------------
  54.         Map<String, DummyObj> mapRes = Stream.concat(dataToBeAdded.stream(), dataToBeSubtracted.stream().map(obj -> {
  55.                     obj.setAttr4(-1 * obj.getAttr4());
  56.                     return obj;
  57.                 }))
  58.                 .collect(Collectors.toMap(obj -> String.format("%s%s%s", obj.getAttr1(), obj.getAttr2(), obj.getAttr3()),
  59.                         Function.identity(),
  60.                         (obj1, obj2) -> new DummyObj(obj1.getAttr1(), obj1.getAttr2(), obj1.getAttr3(), obj1.getAttr4() + obj2.getAttr4())
  61.                 ));
  62.  
  63.         System.out.println("\nOutput w Optimized Solution: ");
  64.         for (DummyObj obj: mapRes.values()){
  65.             System.out.println(obj);
  66.         }
  67.     }
  68.  
  69.     static class DummyObj {
  70.         private String attr1, attr2, attr3;
  71.         private Double attr4;
  72.  
  73.         public DummyObj(String attr1, String attr2, String attr3, Double attr4) {
  74.             this.attr1 = attr1;
  75.             this.attr2 = attr2;
  76.             this.attr3 = attr3;
  77.             this.attr4 = attr4;
  78.         }
  79.  
  80.         public String getAttr1() {
  81.             return attr1;
  82.         }
  83.  
  84.         public void setAttr1(String attr1) {
  85.             this.attr1 = attr1;
  86.         }
  87.  
  88.         public String getAttr2() {
  89.             return attr2;
  90.         }
  91.  
  92.         public void setAttr2(String attr2) {
  93.             this.attr2 = attr2;
  94.         }
  95.  
  96.         public String getAttr3() {
  97.             return attr3;
  98.         }
  99.  
  100.         public void setAttr3(String attr3) {
  101.             this.attr3 = attr3;
  102.         }
  103.  
  104.         public Double getAttr4() {
  105.             return attr4;
  106.         }
  107.  
  108.         public void setAttr4(Double attr4) {
  109.             this.attr4 = attr4;
  110.         }
  111.  
  112.         @Override
  113.         public String toString() {
  114.             return String.format("%s %s %s %g", attr1, attr2, attr3, attr4);
  115.         }
  116.     }
  117. }
Success #stdin #stdout 0.18s 54092KB
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Standard input is empty
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Output w Original Solution: 
uuid1 pqrs mer1 23.0000
uuid3 xyz mer2 -10.0000
uuid2 xyz mer1 18.0000
uuid1 abcd mer1 15.0000

Output w Optimized Solution: 
uuid1 pqrs mer1 23.0000
uuid3 xyz mer2 -10.0000
uuid2 xyz mer1 18.0000
uuid1 abcd mer1 15.0000
https://ideone.com/K5qfsI
How do I subtract two Object Lists based on the attributes?

https://stackoverflow.com/questions/72373297/how-do-i-subtract-two-object-lists-based-on-the-attributes
language:
Java (HotSpot 12)
created:
2 years ago
visibility:
public

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