Javascript merge 2 arrays and sum same key values

Question

I have 2 array:

    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]];

Want to get 1 merged array with the sum of corresponding keys;

    var array1 = [[1,10],[2,10],[3,10],[4,10],[5,50],[6,50],[7,10],[8,10],[9,10]];

Both arrays have unique keys, but the corresponding keys needs to be summed.

I tried loops, concat, etc but can't get the result i need.

anybody done this before?

Answer 1

This is one way to do it:

var sums = {}; // will keep a map of number => sum

// for each input array (insert as many as you like)
[array1, array2].forEach(function(array) {
    //for each pair in that array
    array.forEach(function(pair) {
        // increase the appropriate sum
        sums[pair[0]] = pair[1] + (sums[pair[0]] || 0);
    });
});

// now transform the object sums back into an array of pairs
var results = [];
for(var key in sums) {
    results.push([key, sums[key]]);
}

See it in action.