JavaScript array flatten with an if statment

Question

flatten two array with an if statment I have array1 and array2 I want array3

<script>
    var array1 = [[5,10],[6,10],[7,10],[8,10],[9,10]];
    var array2 = [[1,10],[2,10],[3,10],[4,10],[5,40],[6,40]];

    // only the second number will add if they are different
    // [5,10] + [5,40] 
    // [6,10] + [6,40]

    // array3 = [[1,10],[2,10],[3,10],[4,10],[5,50],[6,50],[7,10],[8,10],[9,10]];

</script>

Step 1: Use a better structure (for example a Map). Step 2: it's now trivial — Denys Séguret, Apr 21 '16 at 13:41
Possible duplicate of [JavaScript array difference](http://stackoverflow.com/questions/1187518/javascript-array-difference) — Tim B, Apr 21 '16 at 13:42
Where's the effort? Did you even attempt to solve this yourself? — Brett, Apr 21 '16 at 13:44

Nina Scholz · Accepted Answer · 2016-04-22T09:04:49.633

This is a proposal with Array#forEach() in a single loop and a temporary object.

var array1 = [[5, 10], [6, 10], [7, 10], [8, 10], [9, 10]],
    array2 = [[1, 10], [2, 10], [3, 10], [4, 10], [5, 40], [6, 40]],
    array3 = [];

array2.concat(array1).forEach(function (a) {
    if (!this[a[0]]) {
        this[a[0]] = [a[0], a[1]];
        array3.push(this[a[0]]);
        return;
    }
    if (this[a[0]][1] !== a[1]) {
        this[a[0]][1] += a[1];
    }
}, Object.create(null));


document.write('<pre>' + JSON.stringify(array3, 0, 4) + '</pre>');

Solution with for loop

var array1 = [[5, 10], [6, 10], [7, 10], [8, 10], [9, 10]],
    array2 = [[1, 10], [2, 10], [3, 10], [4, 10], [5, 40], [6, 40]],
    array3 = [],
    i, 
    temp = Object.create(null),
    array = array2.concat(array1);

for (i = 0; i < array.length; i++) {
    if (!temp[array[i][0]]) {
        temp[array[i][0]] = [array[i][0], array[i][1]];
        array3.push(temp[array[i][0]]);
        continue;
    }
    if (temp[array[i][0]][1] !== array[i][1]) {
        temp[array[i][0]][1] += array[i][1];
    }
}

document.write('<pre>' + JSON.stringify(array3, 0, 4) + '</pre>');

how can i handle this with for in vanilla js – Mohammad Gheydari Apr 22 '16 at 08:56 — Mohammad Gheydari, Apr 22 '16 at 08:56
@MohammadGheydari, please see edit. – Nina Scholz Apr 22 '16 at 09:05 — Nina Scholz, Apr 22 '16 at 09:05

JavaScript array flatten with an if statment

1 Answers1