Uncaught TypeError: Cannot read property '0' of undefined in 3d array

Question

Following is my Code:

        var i,j;
        var period = 5;
        var sec = new Array(new Array(new Array()));
        for(i=0;i<6;i++){
            for(j=1;j<period;j++){  
                sec[j][i][j] = j;
                console.log("SEC: "+j+i+j+" = "+sec[j][i][j]);
                console.log('/n');
            }
        }

When I execute the above code I get cannot read property '0' of undefined at sec[j][i][j] assignment. I don't understand the reason behind it.. It would be great if you guys can help me on this. Thanks in advance.

marvel308 · Accepted Answer · 2017-10-02 06:23:12Z

4

That is because sec[1][0][1] is undefined, you need to push an array every time

        var i,j, period = 6;
        var sec = [];
        for(i=0;i<6;i++){
            for(j=1;j<period;j++){
                sec[j] = [];
                sec[j][i] = [];
                sec[j][i][j] = j;
                console.log("SEC: "+j+i+j+" = "+sec[j][i][j]);
                console.log('/n');
            }
        }

answered Oct 2, 2017 at 6:23

marvel308

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Comments

Peter · Accepted Answer · 2017-10-02 06:24:48Z

1

var sec = new Array(new Array(new Array()));

Doesn't do what you think it does. Try to allocate the inner arrays when needed like this instead

var i, j;
var period = 5;
var sec = [];
for (i = 0; i < 6; i++) {
  for (j = 1; j < period; j++) {
    sec[j] = sec[j] || [];
    sec[j][i] = sec[j][i] || [];
    sec[j][i][j] = j;
    console.log("SEC: " + j + i + j + " = " + sec[j][i][j]);
    console.log('\n');
  }
}

Also, /n prints '/n' not a new line which is \n

answered Oct 2, 2017 at 6:24

Peter

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Comments

Akash Bhandwalkar · Accepted Answer · 2017-10-02 06:20:56Z

0

Although you have declared array as 3D array, JavaScript do not allocate the memory to it.

So being 3D array sec[0] is undefined.

answered Oct 2, 2017 at 6:20

Akash Bhandwalkar

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2 Comments

Yash Parekh Over a year ago

so if I am not using sec[0] at all how do I proceed?

Akash Bhandwalkar Over a year ago

Refer @peter solution

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