Look through every items in array(A) and check if it allready exsists in another array(B)

Question

I have two arrays(arrayA & arrayB). I want to check if any of the items in arrayA allready exists in arrayB. if it doesn't I want to add it to arrayB(but that's not the problem). In the exampel I just want to console.log that I'm adding the item to array B.

First I thought this was a good idea:

 for(var i = 0; i < arrayA.length; i++){
        for (var j = 0; j < arrayB.length; j++) {
            if(body[i].id == res[j].name){
                console.log("The article allready exsists")
            }
            else{
                console.log("Adding item to arrayB")
            }


      }

      }

Then I realised that this wasn't a verry good way to do it because the array's are pretty big. Also the else-statement will be ran the number of times equal to the length of arrayA. Also It's a problem because the first time this will run the array length of arrayB will be zero and wont even reach the else-statement.

Is their any other ways to achive what I'm trying to do here?

you can store (push) the missing values in another array(C), then concat it to array B after the for loops are done — stackoverflow, Mar 31 '17 at 07:26
So if I understand right, you want to push unique items in `ArrayB`. Right? — Rajesh, Mar 31 '17 at 07:29
Have you checked this link: http://stackoverflow.com/questions/11246758/how-to-get-unique-values-in-an-array — Rajesh, Mar 31 '17 at 07:34
@Alexandru-IonutMihai Not my vote. I comment when I downvote — Rajesh, Mar 31 '17 at 07:36

score 3 · Answer 1 · answered Mar 31 '17 at 07:35

You could use a hash table and a linear approach by iterating first arrayB and collect the name property and then iterate over arrayA and check if the id is in arrayB with the hash table. Add the information to arrayB if not exist.

var arrayA = [{ id: 1 }, { id: 3 }, { id: 4 }, { id: 6 }, { id: 7 }, { id: 9 }, { id: 12 }, { id: 35 }, { id: 22 }, { id: 11 }, { id: 34 }, { id: 90 }, { id: 2 }],
    arrayB = [{ name: 1 }, { name: 7 }, { name: 8 }, { name: 19 }, { name: 25 }, { name: 41 }, { name: 35 }, ],
    hashB = Object.create(null);

arrayB.forEach(function (b) {
    hashB[b.name] = true;
});

arrayA.forEach(function (a) {
    if (!hashB[a.id]) {
        arrayB.push({ name: a.id });
        hashB[a.id] = true;
    }
});

console.log(arrayB);

.as-console-wrapper { max-height: 100% !important; top: 0; }

Kinda over my level, not familiar with hash tables but will definitively look into it! — WilliamG, Mar 31 '17 at 07:41

score 2 · Accepted Answer · answered Mar 31 '17 at 07:36

2

May be this could help. You donot need nested loops for achieving this.

 var arrayA = [1,2,3,4,5,6];
 var arrayB = [2,4,7,8];
 for(var i = 0; i < arrayA.length; i++){
       if(arrayB.indexOf(arrayA[i]) > -1){
            console.log("The article allready exsists");
         }
         else{
             console.log("Adding item to arrayB")
         }
   }

answered Mar 31 '17 at 07:36

Ankur Agarwal

286
1
5

Doesn't using indexOf count as a nested loop? – Rohit Chatterjee Apr 02 '17 at 05:01

Look through every items in array(A) and check if it allready exsists in another array(B)

2 Answers2

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