Intersect and union of two different list of custom objects with streams

Question

I want to get an intersection and union of two Lists of different types. I have been trying using Java 8 streams because I think this is the easiest way to do it. So far I have failed each time.

I have simplified the code so it can easily be reproduced. I have two objects, Data1 and Data2.

For example:

public class Data2 {    
    private int id;
    private String name;
    private String type;

    public int getId() {
        return id;
    }

    public void setId(int id) {
        this.id = id;
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public String getType() {
        return type;
    }

    public void setType(String type) {
        this.type = type;
    }

    public Data2(int id, String name, String type) {
        this.id = id;
        this.name = name;
        this.type = type;
    }

}

public class Data1 {

    private int id;
    private String name;
    private int amount;

    public int getId() {
        return id;
    }

    public void setId(int id) {
        this.id = id;
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public int getAmount() {
        return amount;
    }

    public void setAmount(int amount) {
        this.amount = amount;
    }

    public Data1(int id, String name, int amount) {
        this.id = id;
        this.name = name;
        this.amount = amount;
    }
}

public class OutputData {
    private int id;
    private String name;
    private String type;
    private int amount;

    public int getId() {
        return id;
    }

    public void setId(int id) {
        this.id = id;
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public String getType() {
        return type;
    }

    public void setType(String type) {
        this.type = type;
    }

    public int getAmount() {
        return amount;
    }

    public void setAmount(int amount) {
        this.amount = amount;
    }

    public OutputData(int id, String name, String type, int amount) {

        this.id = id;
        this.name = name;
        this.type = type;
        this.amount = amount;
    }

}

They have similar fields.. I need to intersect them based on ID (intersect) and store them in an output (union?) of type OutputData.

Example of a main type:

List<Data2> listOfData2 = new ArrayList<Data2>();

    listOfData2.add(new Data2(10501, "JOE"  , "Type1"));
    listOfData2.add(new Data2(10603, "SAL"  , "Type5"));
    listOfData2.add(new Data2(40514, "PETER", "Type4"));
    listOfData2.add(new Data2(59562, "JIM"  , "Type2"));
    listOfData2.add(new Data2(29415, "BOB"  , "Type1"));
    listOfData2.add(new Data2(61812, "JOE"  , "Type9"));
    listOfData2.add(new Data2(98432, "JOE"  , "Type7"));
    listOfData2.add(new Data2(62556, "JEFF" , "Type1"));
    listOfData2.add(new Data2(10599, "TOM"  , "Type4"));


List<Data1> listOfData1 = new ArrayList<Data1>();

    listOfData1.add(new Data1(10501, "JOE"    ,3000000));
    listOfData1.add(new Data1(10603, "SAL"    ,6225000));
    listOfData1.add(new Data1(40514, "PETER"  ,2005000));
    listOfData1.add(new Data1(59562, "JIM"    ,3000000));
    listOfData1.add(new Data1(29415, "BOB"    ,3000000));

Here is one of my best attempts at this, with no success and lots of errors:

List<OutputData> od = 
  listOfData1.stream()
             .flatMap(x -> listOfData2.stream()
                                      .filter(y -> x.getId().equals(y.getId()))
             .map(y -> new OutputData(x.getId(), x.getName(), y.getType(), x.getAmount()))
             .collect(Collectors.toList()));

This should return a List<OutputData> that has one entry of ID 10603, name SAL and all other fields populated.

Are you using Guava?

shmosel
– shmosel

2016-12-16 20:28:37 +00:00
Commented Dec 16, 2016 at 20:28 — shmosel
– shmosel, Commented Dec 16, 2016 at 20:28
I am not, but I would be open to it

gd000
– gd000

2016-12-16 20:38:43 +00:00
Commented Dec 16, 2016 at 20:38 — gd000
– gd000, Commented Dec 16, 2016 at 20:38

Ran Koretzki · Accepted Answer · 2016-12-16 20:49:05Z

7

This should do it, but in the example there are 5 records in each list that have same ids.

List<OutputData> result = listOfData1.stream()
        .flatMap(x -> listOfData2.stream()
                .filter(y -> x.getId() == y.getId())
                .map(y -> new OutputData(y.getId(), x.getName(), y.getType(), x.getAmount())))
        .collect(Collectors.toList());

answered Dec 16, 2016 at 20:49

Ran Koretzki

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1 Comment

gd000 Over a year ago

I just realized my test cases were wrong. I am going to test this out and will let you know

Eric · Accepted Answer · 2016-12-16 20:24:44Z

0

I'll give you some pseudo code:

declare list 3 (type data3)

for i = length of list 1
  for j = length of list 2
    if list1[i].getid == list2[j].getid
      new data3 object with all relevant fields
      add to list 3

answered Dec 16, 2016 at 20:24

Eric

6018 silver badges22 bronze badges

2 Comments

gd000 Over a year ago

Thanks for the pseudo code. I am able to do it no problem with regular loops. I wanted to do it using java 8 streams though

Eric Over a year ago

No problem. I was wondering why you were using a more complicated solution than necessary. Cheers!

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