How to remove an array from a multidimensional array if it exists in another multidimensional array?

Question

I have two multidimensional arrays and need to remove all the arrays from array A that exist in array B. I've tried it this way with no luck:

var arrayA = [[0,1], [2,0], [0,3], [4,0], [0,5]];

var arrayB = [[0,1], [0,3]];

arrayA = arrayA.filter( function( el ) {
  return arrayB.indexOf( el ) < 0;
} );

alert(arrayA);

This works when the elements in arrayA and arrayB are single values and but when they are arrays. Not sure what I am doing wrong?

are you sure `indexOf` is for arrays? http://www.w3schools.com/jsref/jsref_indexof.asp — Félix Adriyel Gagnon-Grenier, Oct 29 '14 at 16:11

score 3 · Answer 1 · answered Oct 29 '14 at 16:10

3

Assuming the inner arrays are always in the same order to match:

for (var i = 0; i < arrayA.length; i++) {
    for (var j = 0; j < arrayB.length; j++) {
        if (JSON.stringify(arrayA[i]) == JSON.stringify(arrayB[j])) {
            arrayA.splice(i, 1);
            break;
        }
    }
}

Fiddle: http://jsfiddle.net/o2qk7hjd/

answered Oct 29 '14 at 16:10

tymeJV

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Thanks, but unfortunately the order is not guaranteed to match – user3688241 Oct 29 '14 at 16:19
I used this and it really helped! Just one side note, feel free to use === instead of ==. #eslint – Charlie-Greenman Aug 11 '15 at 01:49

Amit Joki · Answer 2 · 2014-10-29T16:31:58.840

1

You can do it like this

var arr = arrayA.map(function(x){ return x + "" }); // convert the array to string
arrayB.forEach(function(e) {
    var idx = (arr.indexOf(e + "")); // find the index
    arr.splice(idx, 1); // remove it
});
arrayA = arr.map(function(x) { return x.split(","); });

edited Oct 29 '14 at 16:31

answered Oct 29 '14 at 16:13

Amit Joki

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Yury Tarabanko · Accepted Answer · 2014-10-29T16:28:28.720

Array.prototype.indexOf uses strict equals comparison to check if elements are equal. This wont work for reference types since [] === []; is false. You can either use @tymeJV solution which is O(lenA*lenB) complexity or preindex arrayB making it O(lenA + lenB)

Demo.

function index(arr) {
    return arr.reduce(function(acc, item){
        return acc[JSON.stringify(item)] = item, acc
    }, {});    
}
var arrayA = [[0,1], [2,0], [0,3], [4,0], [0,5]];

var arrayB = [[0,1], [0,3]];

var indexB = index(arrayB);

arrayA = arrayA.filter( function( el ) {
  return !(JSON.stringify(el) in indexB);
} );

console.log(arrayA);

UPD If the order of elements inside inner arrays is not quaranteed you can use sort. This will make this task O(lenA*log(lenA) + lenB*log(lenB))

Demo 2.

How to remove an array from a multidimensional array if it exists in another multidimensional array?

3 Answers3

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