2

I wrote a script to remove any null, undefined, 0, false or empty string value using .splice(), but the code has only removed NaN and 0s.

Here is what I tried:

function remove(arr){ // input [NaN, 0, 15, false, -22, '',undefined, 47, null]
    var bin = [];
    for (var i =0; i<arr.length; i++){
        if (arr[i] == (NaN || 0 || false || "" || undefined || null)){
            arr.splice(arr[i],1);
        }
    }
  console.log(arr); // Expected output [15, -22, 47]
}
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5
  • 3
    arr = arr.filter(e => e); Commented Mar 18, 2016 at 4:24
  • 2
    arr = arr.filter(Boolean) is built-in ES5. Commented Mar 18, 2016 at 4:25
  • Possibly duplicate stackoverflow.com/questions/31925323/… Commented Mar 18, 2016 at 4:41
  • Where did you find the syntax x == (a || b || c || d) and what do you expect it to do? Why are you trying to use splice instead of using filter to create a new array? Commented Mar 18, 2016 at 4:53
  • I was trying to check if x is equal to a or b or c or d, I can tell from your comment that it's wrong syntax, would you please explain why? I was using splice because I am new to programming so I didn't know any better Commented Mar 23, 2016 at 3:10

5 Answers 5

Reset to default
3

Problem in code:

  1. Iterate over array from last element to first element
  2. Array#splice expects first argument as index, not the item itself
  3. To check if an element is NaN, use isNaN().
  4. To compare with multiple values, compare the elements individually with each item

Working code:

function remove(arr) {
    for (var i = arr.length - 1; i >= 0; i--) {
        if (isNaN(arr[i]) || arr[i] === 0 || arr[i] === false || arr[i] === "" || arr[i] === undefined || arr[i] === null) {

        // Which is same as
        // if (!arr[i]) {
            arr.splice(i, 1);
        }
    }

    console.log(arr); // Expected output [15, -22, 47]
}

remove([NaN, 0, 15, false, -22, '', undefined, 47, null]);

Use Array#filter

arr = arr.filter(e => e);


var input = [NaN, 0, 15, false, -22, '',undefined, 47, null];

var filteredArr = input.filter(e => e);
document.body.innerHTML = '<pre>' + JSON.stringify(filteredArr, 0, 4) + '</pre>';

Or as said by @dandavis in comment

arr = arr.filter(Boolean);


var input = [NaN, 0, 15, false, -22, '',undefined, 47, null];

var filteredArr = input.filter(Boolean);
document.body.innerHTML = '<pre>' + JSON.stringify(filteredArr, 0, 4) + '</pre>';

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5 Comments

look closer, it does appear that mutation is desired, so splice() might be needed still.
@dandavis Didn't understand your last, but added the code using splice
@Tushar Thanks alot for your answer, I have tried to run your code but only changed the iteration to count from the first element to last but it didn't work, whereas your original method worked, would you please explain why ascending looping will not work?
@MohamedHegazy Ascending order will not work because when used splice the array will be updated and the index on the next element will not work. See this fiddle, in the console some elements(0 and -22) are missed.
@dandavis Mutation is not really desired, I was just solving this exercise so I thought splice would do the job
2

This solution may not be that efficient 

function filterArray(el) {
    return (typeof (el) === "number" && el != 0 && !isNaN(el));
}

arr = [NaN, 0, 15, false, -22, '', undefined, 47, null];
console.log(arr.filter(filterArray));

jsfiddle

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2 Comments

Won't this remove strings?
how about using truthiness? console.log(arr.filter(function(n){return n;}))
2

use lodash.

console.log(_.compact(arr));
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Comments

1

You refer to using splice so I assume you want an in-place (mutating) solution. Here's a simple, quick approach:

function compact(a) {
  var i = 0, j = 0;

  while (i < a.length) {
    var v = a[i++];
    if (v) a[j++] = v;
  }

  a.length = j;
}

In case you care (and you probably shouldn't), this is 10 times faster than a loop over splice. See http://jsperf.com/compacting-an-array.

If you want a solution which creates a new array, the alternatives given in other answers using filter are fine, but here's a basic version:

function compact(a) {
  var i = 0, j = 0, result = [];

  while (i < a.length) {
    var v = a[i++];
    if (v) result[j++] = v;
  }

  return result;
}
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1 Comment

Mutation means you change the input. That's what splice does, and that's how my first sample code works. The alternative to mutation (in-place) is to create a new array with just the values you want. That's how filter works, and also how my second sample code works.
0 
 function bouncer(arr) {
  var newArr=arr.slice(0);
  var n=0;
  for(var i=0; i<arr.length;i++){
    if(arr[i]==false||arr[i]==null||arr[i]==0||arr[i]==""||arr[i]==undefined||Number.isNaN(arr[i])==true){
      newArr.splice(n,1);

    } else n++;
  }
  console.log(newArr);
  return newArr;
}

bouncer([null, NaN, 1, 2, undefined,0,'a']);

I have tried to do it with slice()... For NaN I used the function Number.isNaN() and if returns true goes on... The input was [null, NaN, 1, 2, undefined,0,'a'] and returned [ 1, 2, 'a'] as it is expected... Hope it helped you

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