如果第一个值相同，则Javascript将第二个数组值相加

Question

Sorry if the title isn't that clear. This is kind of hard to explain for me, as I'm not that good when it comes to multiple arrays.

I have an array: [ [21, 1000], [21, 500], [18, 100], [18, 200] ]

Now I want to get this resulting array: [ [21, 1500], [18, 300] ]

How do I go about doing this?

I've tried using 21 and 18 as array keys , but this way I couldn't use the array in a for loop with .length counting. I ended up with a total of 4 arrays to almost get it working.

---

Edit:

I want to avoid using the 21 and 18 values as array keys.

I also want to be able to iterate over the resulting array/object, and use the 21 and 18 "keys" as well, to make some further changes to my page.

Thanks already for all the responses!

Answer 1

How about creating an object :

var arr = [ [21, 1000], [21, 500], [18, 100], [18, 200] ];
    obj = {};

for (i=0; i<arr.length; i++) {
    obj[arr[i][0]] = (obj[arr[i][0]] || 0) + arr[i][1];
}

// obj now equals {18: 300, 21: 1500} 
// obj[21] equals 1500 etc

FIDDLE

You could create an array the same way :

var arr  = [ [21, 1000], [21, 500], [18, 100], [18, 200] ],
    arr2 = [];

for (i=0; i<arr.length; i++) {
    arr2[arr[i][0]] = (arr2[arr[i][0]] || 0) + arr[i][1];
}

// giving you the array [18: 300, 21: 1500]
// where arr2[18] equals 300

Answer 2

You definitely don't need any jQuery for this to get the result array you asked for:

var one = [21, 18];
var two = [ [21, 1000], [21, 500], [18, 100], [18, 200] ];
var results = [];

for(var i in one) {
    results[i] = 0;

    for(var x in two)
        if(two[x][0] === one[i])
            results[i] = results[i] + two[x][1];

    results[i] = [one[i], results[i]];
}

Fiddle here

Answer 3

in case your values are not in order, you can use this:

fiddle:
http://jsfiddle.net/acturbo/YWaja/

javasript:

var array1=    [21, 18];
var array2 =   [ [21, 1000], [21, 500], [18, 100], [18, 200] ];
var result =   [ [0,0], [0,0] ];

for (i=0;i<array1.length;i++){

    result[0,i][0] = array1[i];

    for (j=0;j<array2.length;j++){

        var key = array2[i,j][0];
        var val = array2[i,j][1];

        if (  key == array1[i] ){
            result[0,i][1] += val;
        }
    }
}

Answer 4

Here is another possibility, it is using Array.forEach , so you need to have a modern browser or use one of the many "shims"/"polyfills" out there.

Javascript

var first = [21, 18],
    second = [
        [21, 1000],
        [21, 500],
        [18, 100],
        [18, 200]
    ],
    store = {};
    result = [];


first.forEach(function (element) {
    second.forEach(function (pair) {
        var value;

        if (pair[0] === element) {
            value = store[element] || 0;
            store[element] = value + pair[1];
        }
    });

    if (typeof store[element] === "number") {
        result.push([element, store[element]]);
    }
});

console.log(result);

On jsfiddle

Update: here is a solution based on the updated question, this also uses Object.keys and Array.map to do the conversion from an object to the array format that the OP has requested.

Javascript

var first = [
        [21, 1000],
        [21, 500],
        [18, 100],
        [18, 200]
    ],
    store = {};
    result;

first.forEach(function (pair) {
    store[pair[0]] = (store[pair[0]] || 0) + pair[1];
});

result = Object.keys(store).map(function (key) {
    return [parseInt(key, 10), store[key]];
});

console.log(result);

On jsfiddle

Answer 5

function aggregateResults(indexes, inputArray) {
  var ret = [], tmp;
  for (var i=0; i<indexes.length; i++) {
    tmp = 0;
    for (var j=0; j<inputArray.length; j++) {
      tmp += inputArray[j][0] == indexes[i] ? inputArray[j][1] : 0;
    }
    ret.push([indexes[i], tmp])
  }
  return ret;
}