Function that removes every second element

Question

I want to write a function that removes every second element given that the array is longer than length 2. For instance:

removeEveryOther([1, 2, 3, 4, 5, 6, 7, 8, 9, 10]) returns [1, 3, 5, 7, 9]);
removeEveryOther([[1, 2]]) returns [[1, 2]])

Here is my try:

function removeEveryOther(arr){

  for (i=0; i < arr.length; i++) {
    if (arr.length>2) {
      arr.splice((2*i), 1);
      }
     } 
  return arr
}

When invoked the function:

removeEveryOther(['1', '2', '3', '4', '5', '6', '7']) returns [ '2', '3', '5', '6' ]

Not sure what I'm doing wrong though, thanks for reading or even helping me out. Have a nice day!

2*0 is 0 so 1 is gone => [2,3,4,...], 2*1 is 2 so 4 is gone - try it backwards ;) — Estradiaz, Jun 09 '20 at 08:16
If you want to modify in-place by removing, then you should go backwards because all array items shift after a deletion. You can also just produce a new array with `arr.filter((item, index) => index % 2 == 0)` — VLAZ, Jun 09 '20 at 08:18

score 4 · Answer 1 · answered Jun 09 '20 at 08:18

4

You can use filter. And move the check up to the top:

function removeEveryOther(arr){
  if (arr.length <= 2) {
    return arr
  }

  return arr.filter((a,i) => i%2 == 0);
}

answered Jun 09 '20 at 08:18

Gh05d

7,923
7
33
64

score 1 · Answer 2 · answered Jun 09 '20 at 08:16

1

You should not mutate the original array and rather create a new one.

function removeEveryOther(arr){
  if (arr.length > 2) {
    return arr.filter((item, index) => index % 2 === 0);
  } else {
    return arr;
  }
}

answered Jun 09 '20 at 08:16

amik

5,613
3
37
62

score 1 · Answer 3 · answered Jun 09 '20 at 08:18

1

you can do this:

let removeEvery2 = (arr) => {
    if(arr.length > 2) {
       return arr.filter((el, i) => i % 2 === 0)
    }
   return arr
}

answered Jun 09 '20 at 08:18

Red Baron

7,181
10
39
86

score 1 · Answer 4 · answered Jun 09 '20 at 08:22

You could loop from the end, because with splicing from start all following indices are gone.

function removeEveryOther(array) {
    if (array.length < 3) return array;

    let i = Math.floor(array.length / 2) * 2 + 1;
    while (i > 0) {
        array.splice(i, 1);
        i -= 2;
    }
    return array;
}

console.log(removeEveryOther([1, 2, 3, 4, 5, 6, 7, 8, 9, 10])); // [1, 3, 5, 7, 9]
console.log(removeEveryOther([1, 2]));

score -2 · Answer 5 · answered Jun 09 '20 at 08:18

-2

Try this function, I kept it very simple for your understanding and very near to what you wrote in the question

function removeEveryOther(arr)
{
    if(arr.length <= 2)
        return arr;
     var arr_ret = [];
     for (i=0; i < arr.length; i+=2) 
     {
        arr_ret.push(arr[i])     
     } 
    return arr_ret
}

answered Jun 09 '20 at 08:18

NoobX

125
6

Devote without any explanation. WEIRD! – NoobX Jun 09 '20 at 08:36

score -2 · Accepted Answer · answered Jun 09 '20 at 08:23

Use a simple for loop. Start at index 1 instead of 0 and increment i by 2 instead of 1.

function removeEveryOther(arr){
    if(arr.length <= 2) return arr;
    for(let i = 1; i < arr.length; i +=2){
        arr.splice(i, 1);
    }
    return arr;
}

console.log(removeEveryOther([1, 2, 3, 4, 5, 6, 7, 8]));
console.log(removeEveryOther([1, 2]))

Function that removes every second element

6 Answers6