Q:

add item to an array of json objects

I want to add a value to specific field of my array which is a json object.
in other words i want to append to a json object which is a field of another array.
var cdata = new Array();
 for (i in json2) {
     for (j in json2[i]) {
         //here i get error:
         cdata[j].push({
             'x': json2[i].timestamp,
             'y': json2[i][j]
         });
     };
 };

but i get Uncaught TypeError: Cannot call method 'push' of undefined  error.
thanks in advance

A:

You are calling push on an array element referred to by the index j as follows cdata[j]
You should call 
cdata.push({
         'x': json2[i].timestamp,
         'y': json2[i][j]
     });

Additionally - thanks to commenter - looking at the way you are iterating through the array json2 it doesn't seem right. We could do with seeing json2 to fully answer this one.
The line:
json2[i].timestamp

Suggests json2 is an array of objects
However the line:
json2[i][j] 

suggests json2 is a multi-dimensional array.
See this post: How can I create a two dimensional array in JavaScript?
HTH

