Add or change a value of JSON key with jquery or javascript

Question

I have a JSON string(?) that I have returned from $.ajax() and named it data. Some of the values are empty and I need to

Answer 1

var y_axis_name=[];

 for(var point in jsonData[0].data)
              { 
                y_axis_name.push(point);

              }

y_axis_name is having all the key name

try on jsfiddle