Why are empty items in my array and how do I get rid of them? [duplicate]

问题

I am using Visual Studio Code. I am trying to return an array with only odd numbers using JavaScript. This is the code:

function oddCouple(arr) {
  for (let i = 0; i < arr.length; i++) {
    if (arr[i] % 2 == 0) {
      delete arr[i];
    }
  }
  return arr;
}

console.log(oddCouple([2, 6, 7, 0, 1, 3, 7, 5]));

This is what I am getting. I do not want the empty items, just odd numbers.

[ <2 empty items>, 7, <1 empty item>, 1, 3, 7, 5 ]

回答1:

You need to use splice() instead of delete because delete doesn't change the length of the array. But be careful using splice() in a for loop because you alter the array as you're looping through it, which doesn't work well.

An alternative is to loop backwards:

function oddCouple(arr) {
  for (let i = arr.length - 1; i >= 0; i--) {
    if (arr[i] % 2 == 0) {
      arr.splice(i, 1);
    }
  }
  return arr;
}

console.log(oddCouple([2, 6, 7, 0, 1, 3, 7, 5]));

Of course a still better alternative is to use filter(), but note this doesn't change the original array.

function oddCouple(arr) {
  return arr.filter(i => i % 2)  
}

console.log(oddCouple([2, 6, 7, 0, 1, 3, 7, 5]));

回答2:

The delete operator deletes a property of an object. This is the index with the value for an array. The result is a sparse array.

For getting an array without some items, you could filter the array.

function oddCouple(array) {
    return array.filter(v => v % 2);
}

console.log(oddCouple([2, 6, 7, 0, 1, 3, 7, 5]));

Or if you need the same array reference, then you could use Array#splice and iterate the array from the end, because the index is changing after splicing the item.

function oddCouple(array) {
    var i = array.length;
    while (i--) {
        if (array[i] % 2 === 0) {
            array.splice(i, 1);
        }
    }
    return array;
}

console.log(oddCouple([2, 6, 7, 0, 1, 3, 7, 5]));

回答3:

The delete function removes the content of the item but keeps an empty slot.

You need the splice method to remove an element without leaving an empty slot.

arr.splice(i, 1);

回答4:

You can return the array by filtering truthy values:

function oddCouple(arr) {
  for (let i = 0; i < arr.length; i++) {
    if (arr[i] % 2 == 0) {
      delete arr[i];
    }
  }
  return arr.filter(r=>r);
}

console.log(oddCouple([2, 6, 7, 0, 1, 3, 7, 5]));

Rather, I can do simply:

const arr = [2,6,7,0,1,3,7,5]
console.log(arr.filter(r=>r%2!=0))
//or,
console.log(arr.filter(r=>r%2)) // !=0

来源：https://stackoverflow.com/questions/51688366/why-are-empty-items-in-my-array-and-how-do-i-get-rid-of-them

标签

javascript

arrays

function

for-loop