Rearrange array elements into two new arrays

Question

I have a json-encoded array with 5000 lines all looking like the following:

[2013-01-01 07:00, 10, 50]

In order to draw a jqplot with two y-axis, I need to get two different arrays out of this one looking like the following:

array1: [2013-01-01 07:00, 10]
array2: [2013-01-01 07:00, 50]

What I tried is the following approach but it doesn't seem to work well:

var data= <?php echo json_encode($dataarray); ?>;
var array1= [];  
var array2 = [];

for(var i=0, len=data.length; i<len; i++){
  array1[i] = array1[i][0]+array1[i][1];
  array2[i] = array2[i][0]+array2[i][2];
};

Could somebody help or is there even an easier way to draw the 2-y-axis plot with my original array, without the need to split the array elements?

Answer 1

Assuming they are all in an array and that the items are all the same shape, you could use the following piece of code:

var data = [
  ['2013-01-01 07:00', 10, 50],
  ['2013-01-01 08:00', 20, 70]
]

var array1 = data.map(function(item){ return [item[0], item[1]]});
var array2 = data.map(function(item){ return [item[0], item[2]]});

Alternatively, you could change your original approach:

var array1 = [];  
var array2 = [];

for(var i=0, len=data.length; i<len; i++){
  array1.push([data[i][0], data[i][1]]);
  array2.push([data[i][0], data[i][2]]);
};

Finally, i think arrays are usually better to store the same kind of items. Your original data might better suited to be structured like this:

var data = [
  { date: '2013-01-01 07:00', first : 10, second: 50},
  { date: '2013-01-01 07:00', first : 20, second: 70}
]

The same solution works with only minor modifications.

Answer 2

Here is O(n) time complexity approach:

var data= <?php echo json_encode($dataarray); ?>;
var array1 = [];  
var array2 = [];

var len = data.length;
for (i = 0; i < len; i++) {
    array1.push([data[i][0], data[i][1]]);
    array2.push([data[i][0], data[i][2]]);
}