Using javascript forEach and splice on multidimensional array

Question

I'm trying to loop over some data that look like this:

[0]['fields']['status']['name'] = 'In progress'
[1]['fields']['status']['name'] = 'In progress'
[2]['fields']['status']['name'] = 'In review'
[3]['fields']['status']['name'] = 'In progress'
[4]['fields']['status']['name'] = 'In review'

I'm using the following foreach loop to splice all useless indexes, in this case all of them.

issues.forEach(function (item, index) {
   if (issues[index]['fields']['status']['name'] !== "Done") {
       issues.splice(index, 1);
   }
});

If I loop over the array later I can output 'In progress' and 'In review' which is weird because they should be unset. I think this happens because I manipulate the array while using it. Could someone explain what's wrong and how this can be avoided.

You're splicing while moving forward. Splicing will remove an item and then re-order all following items. So, if you have array ["a", "b", "c", "d"] and splice index = 0 you get rid of "a" and you're left with ["b", "c", "d"]. Next time the callback will be called with index = 1 so you remove the wrong item. — VLAZ
– VLAZ, Commented Jan 27, 2020 at 13:12

Nina Scholz · Accepted Answer · 2020-01-27 13:12:22Z

4

Just loop from the end with an index.

This prevents unseen indices and keeps the index where it belongs to.

var index = issues.length;

while (index--) {
    if (issues[index].fields.status.name !== "Done") {
        issues.splice(index, 1);
    }
}

answered Jan 27, 2020 at 13:12

Nina Scholz

388k26 gold badges367 silver badges417 bronze badges

Sign up to request clarification or add additional context in comments.

Comments

Mihai Alexandru-Ionut · Accepted Answer · 2020-01-27 13:12:35Z

3

One possible solution is replacing forEach method with a while loop because when you're using splice, this will modify the issues array inplace and you skip some elements.

I demonstrated this in the following example.

let arr = [1,2,3,4]
arr.forEach((item, index) => {
  arr.splice(index, 1);
});
console.log(arr);

Solution

let i = 0;
while(i < issues.length){
   if (issues[i]['fields']['status']['name'] !== "Done") {
       issues.splice(i, 1);
   }
   else i++;
}

answered Jan 27, 2020 at 13:12

Mihai Alexandru-Ionut

48.6k14 gold badges106 silver badges132 bronze badges

Collectives™ on Stack Overflow

Using javascript forEach and splice on multidimensional array

2 Answers 2

Comments

Comments

Your Answer

Linked

Hot Network Questions

Collectives™ on Stack Overflow

2 Answers 2

Comments

Comments

Your Answer

Sign up or log in

Post as a guest

Linked

Related