An array full of zeros

Question

I am writing a program in JavaScript where you input a number n and it returns an array M that is a list of length 'n' and each element of the list is a different list ele that is also length n and has every element equal to zero. This is my function:

var zeros=function(n){
    var M=[];
    var ele=[];
    for (var q=0; q<n; q++){
        ele.push[q]=0;
    }
    for (var p=0; p<n; p++){
        M.push[p]=ele;
    }
    return M;
};

My problem is that ele always remains undefined no matter how I try to change it. Can anyone tell me why this is happening and how to fix it?

ele.push[q]=0; -> either ele[q]=0; or ele.push(0);. Same with M.push[p]=ele; — VLAZ
– VLAZ, Commented Mar 11, 2021 at 14:18
Actually after a second look M.push[p]=ele; shouldn't be done that way at all because you'll assign the same array to every index in M. The easiest thing is to make Array.from({length: n}, () => Array(n).fill(0)) — VLAZ
– VLAZ, Commented Mar 11, 2021 at 14:20
Oops, guess I just forgot how .push works. :) My bad. Thanks — Joshua
– Joshua, Commented Mar 11, 2021 at 14:24
You say "ele always remains undefined". You're not returning it. That variable only exists while the function is running. — Scott Sauyet
– Scott Sauyet, Commented Mar 11, 2021 at 14:35

klaas0 · Accepted Answer · 2021-03-11 14:28:43Z

3

You can't use push like this Array.push[x]. if you use push on an array it always puts that item to the end of the array (https://www.w3schools.com/jsref/jsref_push.asp). so you can use:

ele.push(0);

OR

ele[q] = 0

answered Mar 11, 2021 at 14:28

klaas0

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Comments

Peter Seliger · Accepted Answer · 2021-03-11 15:58:39Z

0

create a non sparse Array of custom length
map each array item (the undefined value) into
- 2a) a new sparse Array of custom length
- 2b) immediately filled with the custom value.

function squareMatrix(n, value) {
  return Array

    // creates a non sparse, thus iterable, array 
    // which features n-times the undefined value.
    .from({ length: n })

    // thus, one can map over each item.
    .map((item, idx) =>

      // creates a sparse array of custom length `n` which
      // immediately after gets filled with the custom `value`.
      Array(n).fill(value)
    );
}

console.log(
  'squareMatrix(2, 0) ...',
  squareMatrix(2, 0)
);
console.log(
  "squareMatrix(3, '👍🏻')",
  squareMatrix(3, '👍🏻')
);

.as-console-wrapper { min-height: 100%!important; top: 0; }

edited Mar 11, 2021 at 15:58

answered Mar 11, 2021 at 14:36

Peter Seliger

13.5k3 gold badges31 silver badges45 bronze badges

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