Javascript：按键求和多个数组的最有效方法

Question

I have a JSON object returned from a web service, which is an array of objects. I need to add the "data" arrays together to form a summed array. The JSON response looks like this:

[  
  {  
    "data":[  
       0,3,8,2,5
    ],
    "someKey":"someValue"
  },
  {  
    "data":[  
       3,13,1,0,5
    ],
    "someKey":"someOtherValue"
  }
]

There could be N amount of objects in the array. The desired output for the above example would be:

[3, 16, 9, 2, 10]

I was intending on creating an empty array variable (var arr), then looping over the objects, and for each object, loop through the "data" key and for each key increment the corresponding key in arr by the value.

Is there a more efficient way of doing this using some sort of merge function?

Answer 1

How about this, I believe it should work for all cases.

 var data = [{ "data": [ 0, 3, 8, 2, 5 ], "someKey": "someValue" }, { "data": [ 3, 13, 1, 0, 5 ], "someKey": "someOtherValue" }]; var datas = data.reduce(function(a, b) { b.data.forEach(function(x, i) { a[i] = a[i] || 0; a[i] += x; }); return a; }, []); console.log(datas); 

Answer 2

If every object has the same data length, you can try with:

var input; // Your input data
var output = [];
for (var i = 0; i < input[0].data.length; i++) {
  output[i] = input.reduce(function(prev, item) {
    return +(item.data[i]) + prev;
  }, 0);
}

console.log(output);
// [3, 16, 9, 2, 10]

If every object has different data size:

var input; // Your input data
var i = 0, output = [];
while (true) {
  var outOfIndex = true;

  var sum = input.reduce(function(prev, item) {
    if (item.data[i] !== undefined) {
      outOfIndex = false;
    }
    return +(item.data[i]) + prev;
  }, 0);

  if (outOfIndex) {
    break;
  }
  output[i++] = sum;
}

console.log(output);
// [3, 16, 9, 2, 10]

Answer 3

Slightly less imperative solution:

//zip takes two arrays and combines them per the fn argument
function zip(left, right, fn) {
   var shorter = (right.length > left.length) ? left : right;
   return shorter.map(function(value, i) {
       return fn(left[i], right[i]);
   });
}

//assuming arr is your array of objects. Because were using
//zip, map, and reduce, it doesn't matter if the length of the
//data array changes
var sums = arr
    .map(function(obj) { return obj.data; })
    .reduce(function(accum, array) {

        //here we want to combine the running totals w/the current data
        return zip(accum, array, function(l, r) { return l + r; });
    });