Filling a 2D array with 0s in JavaScript

Question

I've been trying to fill up a 2D array with JavaScript and I keep crashing my browser so I assume I have infinite recursion but I can't seem to find my error. Here's my code:

//The two sequences to compare
var sequence1 = "ATTGCTGACTTCA"
var sequence2 = "ATGCTACTA"
  //Creates multi-dimensional array dependent on sequence lengths
var arr = new Array(sequence1.length + 1)
for (i = 0; i < sequence1.length + 1; i++) {
  arr[i] = new Array(sequence2.length + 1);
}
//Fills array with 0s
for (i = 0; i < arr.length; i++) {
  var col = i;
  for (i = 0; i < arr[col].length; i++) {
    arr[col][i] = 0;
  }
}

lei liu · Accepted Answer · 2016-04-04 03:16:49Z

2

When you filling your array, you change the value of i by inner loop， and did not change it back to it's original value after the inner loop! Dont use the same variable name in outer and inner loops!

for (i = 0; i < arr.length; i++) {
  var col = i;
  for (i = 0; i < arr[col].length; i++) {
    arr[col][i] = 0;
  }
  i = col;
}

what you realy should do:

for (i = 0; i < arr.length; i++) {
  for (j = 0; j < arr[i].length; j++) {
    arr[i][j] = 0;
  }
}

answered Apr 4, 2016 at 3:16

lei liu

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Comments

Tushar · Accepted Answer · 2016-04-04 03:14:56Z

1

You can use Array#from, Array#map and Array#fill.

var arr = Array.from({
    length: sequence1.length + 1
}).map(() => Array.from({
    length: sequence2.length + 1
}).fill(0));

var sequence1 = "ATTGCTGACTTCA",
    sequence2 = "ATGCTACTA";

//Creates multi-dimensional array dependent on sequence lengths
var arr = Array.from({
    length: sequence1.length + 1
}).map(() => Array.from({
    length: sequence2.length + 1
}).fill(0));

console.log(arr);

Explanation:

var arr = Array.from({
    length: sequence1.length + 1
})
// Create an array of passed `length` of `undefined` elements

// map will iterate over all the elements of the array and update the value of each element
// Create new array and use this as the individual item in the main array
.map(() => Array.from({
    length: sequence2.length + 1
}).fill(0));

edited Apr 4, 2016 at 3:14

answered Apr 4, 2016 at 3:08

Tushar

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2 Comments

zerkms Over a year ago

The outer array will be filled with the sequence1.length + 1 references to the same nested array. Check the arr[0][0] = 42; console.log(arr[1][0]);

Tushar Over a year ago

@zerkms Thanks for pointing. I forgot about array references. Used map now. :)

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