How to merge 2 ArrayList<HashMap<String, String>> into 1, based on key values?

Question

I have 2 ArrayList < HashMap < String, String>>.

list1: [{name=Alice, count=193}, {name=Bob, count=13}, {name=Charlie, count=179}, ...]

list2: [{name=Alice, change=1}, {name=Bob, change=15}, {name=Jimmy, change=15}, ...]

All key values present in list2 are present in list1, but not vice versa. For eg. since Charlie has 0 change, he is not present in list2. I want to merge these 2 lists based on the key values (name) to create a new list3.

list3: [{name=Alice, count=193, change=1}, {name=Bob ,count=13, change=15}, {name=Charlie, count=179, change=0}, ...]

Why are you using a list of key-value pairs? Shouldn't you be using a simple Map instead? — bcsb1001
– bcsb1001, Commented Nov 24, 2017 at 2:57
The data is from a json source so i just parsed it and put it into a HashMap — Exynos SnapDragon
– Exynos SnapDragon, Commented Nov 24, 2017 at 3:11

NAK · Accepted Answer · 2017-11-24 09:31:03Z

2

Assuming list1 and list2 do not contain duplicate names you can do something like this:

    //list3 created.
    for(HashMap<String,String> hm2:list2){
        String nameValue=hm2.get("name");
        for(HashMap<String,String> hm1:list1){
            if(hm1.get("name").equalsIgnoreCase(nameValue)){
                HashMap<String,String> tempMap = new HashMap();
                tempMap.put("name",nameValue);
                tempMap.put("count",hm1.get("count"));
                tempMap.put("change",hm2.get("change"));
                list3.add(tempMap);
                break;
            }
        }

    }
    System.out.println(list3);

answered Nov 24, 2017 at 9:31

NAK

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Comments

Chanh Hua · Accepted Answer · 2017-11-24 03:24:46Z

0

You can:

1/ create a class called Account which contains name, count, change, then the result would be a list of Account (if you dont want to create a new class, you can skip this step)

2/ from list2 build a HashMap<String (name), Integer (change)>

3/ iterate through the list1, which every element, find a corresponding change base on the HashMap built in step 2, then build an Account (or a HashMap which contains all the info), add the account (or the HashMap) to list3

edited Nov 24, 2017 at 3:24

answered Nov 24, 2017 at 3:09

Chanh Hua

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