Sum of values from array of objects

Question

I have a javascript matrix array with the following structure (the first index is x, the second index is y, so every x item has 4 y items):

0 
  0 { x: 0, y: 0, z: 0}
  1 { x: 0, y: 1, z: 5}
  2 { x: 0, y: 2, z: 0}
  3 { x: 0, y: 3, z: 1}
1
  0 { x: 1, y: 0, z: 4}
  1 { x: 1, y: 1, z: 5}
  2 { x: 1, y: 2, z: 1}
  3 { x: 1, y: 3, z: 8}

What I need to do is get an array that stores the z values per y value. So for all the values of x I need the total values of z arranged by y. The structure I am looking for (assuming 4 y values)

I tried this:

count = [];
    $.each(matrix, function(i, j) {
      $.each(j, function(k, v) {
        count[k] += v["z"];
      })          
    });

But this returns just an array with NaN values. Does anyone have better suggestions?

Where are your array `var` definitions? Must they be arrays or can they be objects? — DevlshOne, Sep 15 '14 at 11:11

Pranav C Balan · Accepted Answer · 2014-09-15T13:15:42.397

1

You need to initialize count array

var count=[ 0, 0, 0, 0];
$.each(matrix, function(i, j) {
  $.each(j, function(k, v) {
    count[k] += parseInt(v["z"],10);
  })          
});

edited Sep 15 '14 at 13:15

answered Sep 15 '14 at 11:11

Pranav C Balan

113,687
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Great, now could I initialize the `count` automatically with the length of the `y` array? So that I don't have to enter another `0` if the `y` array gains an item? – Christian-G Sep 15 '14 at 11:26
Never mind, I came across this: http://stackoverflow.com/questions/1295584/most-efficient-way-to-create-a-zero-filled-javascript-array – Christian-G Sep 15 '14 at 11:34

score 0 · Answer 2 · answered Sep 15 '14 at 11:18

0

Your count array is not initialized, and you are trying to do math with undefined, so your result is NaN. Initialize count array with zeros.

answered Sep 15 '14 at 11:18

Erdogan Kurtur

3,630
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Sum of values from array of objects

2 Answers2