Javascript: Array overriding the same values after assinging to JSON object

Question

I am working with jquery ajax & the ajax response is multidimensional json array, I am assinging the JSON values to coordinates array & then assinging coordinates array to new JSON coord_set, after assinging all values to coord_set, It takes last array values to all,

for e.g. the JSON result contains following values

obj[0]={125, 343, 456, 453},
obj[1]={345, 657, 234, 787},
obj[2]={980, 677, 657, 568}

after assinging to new JSON the values are:

coord_set[0] = {
                    fillColor : 'rgba(255, 234, 111 ,0.5)', 
                    data : [980, 677, 657, 568]
               }
coord_set[1] = {
                    fillColor : 'rgba(255, 234, 111 ,0.5)', 
                    data : [980, 677, 657, 568]
               }
coord_set[2] = {
                    fillColor : 'rgba(255, 234, 111 ,0.5)', 
                    data : [980, 677, 657, 568]
               }

This is my code:

  var obj = JSON.parse(data);
  for(var j=0;j<obj.length;j++)
  { 
      for (var i=0;i<obj[j].length;i++)
      {
                  coordinates[i] = obj[j][i].how_many;
      }

      coord_set[j] = { fillColor : 'rgba(255, 234, 111 ,0.5)', data : coordinates };
  }
  alert(JSON.stringify(coord_set));

Please tell me, If I am doing Anything wrong in my code?

Are you getting an error? You didn't mention what problem you were having. — dwerner
– dwerner, Commented Aug 19, 2013 at 5:38
Not getting any error, the problem is last array of ie. obj[2] values are getting assigned to all coord_set JSON array — K P
– K P, Commented Aug 19, 2013 at 5:42

ruakh · Accepted Answer · 2013-08-19 05:40:48Z

2

The problem is that you're using a single coordinates array. You keep setting and re-setting the values in that same array, and you keep storing that same array in new elements of coord_set. To fix this, you just need to use a new coordinates array on each pass through the outer loop:

  for(var j=0;j<obj.length;j++)
  { 
      coordinates = [];      // <----- add this
      for (var i=0;i<obj[j].length;i++)

answered Aug 19, 2013 at 5:40

ruakh

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2 Comments

fabien Over a year ago

don't forget to make it a local variable, otherwise, you may have other surprises later...

n_g Over a year ago

Thanks a lot ruakh!!! Your fix made my day...... was stuck in this for the entire day today.....

fabien · Accepted Answer · 2013-08-19 05:40:15Z

0

I'm gonna assume that JSON.parse actually works... but since you said you are using jquery, i would use http://api.jquery.com/jQuery.parseJSON/ personally...

Few things about your code:

you never create a new object for coordinates, which is, by default, a global variable in JS. You must type:
```
var coordinates = []; // before the for (var i = 0; ...
```
where is this property "how_many" coming from? I don't see it in your first block of code... The code in your i loop should be:
```
coordinates[i] = obj[j][i];
```

finally, why do you need a copy of this transient object anyway? That should just do it:

coord_set[j] = { fillColor : 'rgba(255, 234, 111 ,0.5)', data : obj[j] };
// if you change your result set to give a code like that:
obj[0]= [ 125, 343, 456, 453 ] // and not: obj[0]={125, 343, 456, 453}

answered Aug 19, 2013 at 5:40

fabien

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1 Comment

ruakh Over a year ago

From the OP's posted output, I'm assuming that the how_many stuff is actually fine. Probably the reason for copying the object is that the JSON stores the individual values in objects containing fields named how_many, whereas the OP just wants the values directly in data.

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