Question 211356 in Javascript Question posted in
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JavaScript: Insert elements into array for every n elements

I would like to insert element into 2nd and 9th position of an array for every 10 elements and the length of array can be vary.
I tried to use mod but the element will be inserted multiple time within 10 elements.

Example:

var array = ['a1', 'a2', 'a3', 'a4', 'a5', 'a6','a7', 'a8', 'a9', 'a10','a11', 'a12', 'a13', 'a14', 'a15', 'a16', 'a17', 'a18', 'a19', 'a20', 'a21', 'a22', 'a23'];

Expected outcome (inserted b & c at position 2nd & 9th ):

[‘a1’, ‘b1‘, ‘a2’, ‘a3’, ‘a4’, ‘a5’, ‘a6′,’a7’, ‘c1‘, ‘a8’, ‘a9’, ‘b2‘, ‘a10′,’a11’, ‘a12’, ‘a13’, ‘a14’, ‘a15’, ‘c2‘, ‘a16’, ‘a17’, ‘b3‘, ‘a18’, ‘a19’, ‘a20’, ‘a21’, ‘a22’, ‘a23’];

How to achieve the result?

Tags:

2

Answers


  1. 0 
    const array = ['a1', 'a2', 'a3', 'a4', 'a5', 'a6', 'a7', 'a8', 'a9', 'a10', 'a11', 'a12', 'a13', 'a14', 'a15', 'a16', 'a17', 'a18', 'a19', 'a20', 'a21', 'a22', 'a23'];
const prefix = new Map([[1, 'b'], [8, 'c']]);
const result = array.flatMap((element, index) => {
  const p = prefix.get(index % 10);
  if (p) {
    return [p + Math.ceil(index / 10), element];
  }
  return element;
});
console.log(result);
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  2. 0

    You can iterate over the array while adding elements with Array#splice.

    const array = ['a1', 'a2', 'a3', 'a4', 'a5', 'a6','a7', 'a8', 'a9', 'a10','a11', 'a12', 'a13', 'a14', 'a15', 'a16', 'a17', 'a18', 'a19', 'a20', 'a21', 'a22', 'a23'];
const prefix = new Map([[1, 'b'], [8, 'c']]);
for (let i = 0; i < array.length; i++) {
  const p = prefix.get(i % 10);
  if (p) array.splice(i, 0, p + Math.ceil(i / 10)), ++i;
}
console.log(array);
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