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)

0 4
1 10
2 1
3 9

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?

• DevlshOne: Where are your array var definitions? Must they be arrays or can they be objects?

Answer 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);
 }) 
});

• Christian-G: 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: Never mind, I came across this: stackoverflow.com/questions/1295584/…

Answer 2

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.