Question 240905 in Javascript Question posted in
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Javascript – How to split the rows in the array using match()?

I have a matrix containing arrays of rows.

let matrix=[['hello'],['world']];

I’m duplicating rows.

matrix=matrix.map(x=>String(x).repeat(2)).map(x=>x.match(new RegExp??))

I want to get

[['hello','hello'],['world','world']]
Tags:

2

Answers


  1. 0

    If you want to duplicate the arrays, you can use concat

    const matrix = [
  ['hello'],
  ['world']
];
const res = matrix.map(a => a.concat(a))
console.log(res);

    Or given that you have an array of arrays and you want to get an N number of entries instead of 1:

    const matrix = [
  ['hello'],
  ['world']
];
const res = matrix.map(a => Array(4).fill(...a));
console.log(res);
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  2. 0

    Your code wouldn’t work. First there’s no Array::repeat() method, second there’s no any sense to use RegExp::match() to duplicate an array, third you’re trying to assign to a const variable. Use simpler tools.

    Since you overwrite the original array you can just mutate it:

    const matrix = [
  ['hello'],
  ['world']
];
// push array into itself thus duplicating it
matrix.forEach(arr => arr.push(...arr));
console.log(matrix);

    That would be definitely faster than overwriting with a new array:

    enter image description here

    <script benchmark data-count="5000000">

// @benchmark The fourth bird
{
let matrix = [
  ['hello'],
  ['world']
];
matrix = matrix.map(a => a.concat(a))
}

// @benchmark Alexander
{
const matrix = [
  ['hello'],
  ['world']
];

matrix.forEach(arr => arr.push(...arr));
matrix;
}
</script>
<script src="https://cdn.jsdelivr.net/gh/silentmantra/benchmark/loader.js"></script>
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