Grouping list of objects where each object is 2 elements array

Question

List<Object[]> values =  query.getResultList();
    //values = [obj1,obj2,obj3]
    //obj1 = "1", "01";
    //obj2 = "1", "02";
    //obj3 = "1:, "03";

Map<String, List<String>> resultMap = values.stream().collect(Collectors.groupingBy(???));

I need a map grouped as - {"1",["01","02","03"]}

I have seen few references but nothing seems to work. what should i put in place of "???" ? if you need anything else , kindly comment. Thanks in advance.

ref :

Shortcut for adding to List in a HashMap

groupingby list of arrays

Why don't you keep it as a `List` or `String[][]`. Apart from that each object is a 2 element array, it is not a 2-D array. — Ravindra Ranwala, Sep 09 '20 at 06:47
because i need the map as i mentioned.only one element is need as list which won't be possible with what u suggested,right ? — Sidharth K.Burnwal, Sep 09 '20 at 07:13

score 2 · Accepted Answer · answered Sep 09 '20 at 07:03

If your object[] is the string[].I think the code is this:

package com.test.dal;

import java.util.Arrays;
import java.util.List;
import java.util.Map;
import java.util.stream.Collectors;

public class LTest {

    public static void main(String[] args) {
        List<String[]> values = getResultList();
        //values = [obj1,obj2,obj3]
        //obj1 = "1", "01";
        //obj2 = "1", "02";
        //obj3 = "1:, "03";

        Map<String, List<String>> resultMap = values.stream().collect(Collectors.groupingBy(o -> ((String[]) o)[0], Collectors.mapping(o -> ((String[]) o)[1], Collectors.toList())));
        System.out.println(resultMap);
    }

    public static List<String[]> getResultList() {
        String[][] inits = {
                {
                        "1", "01"
                }, {
                "1", "02"
        }, {
                "1", "03"
        }
        };
        List<String[]> tbList = Arrays.asList(inits);
        return tbList;
    }
}

i changed as you suggested.but why its giving me this exception : java.lang.ClassCastException: [Ljava.lang.Object; cannot be cast to [Ljava.lang.String; — Sidharth K.Burnwal, Sep 09 '20 at 11:03
Because query.getResultList() is returning a list of object. — Sidharth K.Burnwal, Sep 09 '20 at 11:40

Grouping list of objects where each object is 2 elements array

1 Answers1

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