How do I compare two arrays in nodejs

Question

Say I have two arrays

["a", "b", "c"]

["c", "a", "b"]

What is the best way to compare these two arrays and see if they are equal (they should come as equal for the above scenario)

possible duplicat of http://stackoverflow.com/questions/13523611/how-to-compare-two-arrays-in-node-js — KKK, Apr 02 '14 at 13:17
Clearly a duplicate; the only missing link is pre-sorting both compared arrays first. — raina77ow, Apr 02 '14 at 13:19
@pronox That solution doesn't work > var arr1 = ["a","b","c"]; undefined > var arr2 = ["c","a","b"]; undefined > if (arr1.length == arr2.length ... && arr1.every(function(u, i) { ..... return u === arr2[i]; ..... }) ... ) { ... console.log(true); ... } else { ... console.log(false); ... } false — bluesman, Apr 02 '14 at 13:22
then how is it marked accepted and up voted few times, let me check i — KKK, Apr 02 '14 at 15:21
@pronox There was a missing step to sort the array as thefourtheye showed in his solution — bluesman, Apr 03 '14 at 08:10

thefourtheye · Answer 1 · 2014-04-02T13:55:02.297

4

function compareArrays(array1, array2) {
    array1 = array1.slice();
    array2 = array2.slice();
    if (array1.length === array2.length) {       // Check if the lengths are same
        array1.sort();
        array2.sort();                           // Sort both the arrays
        return array1.every(function(item, index) {
            return item === array2[index];       // Check elements at every index
        });                                      // are the same
    }
    return false;
}

console.assert(compareArrays(["a", "b", "c"], ["c", "a", "b"]) === true);

edited Apr 02 '14 at 13:55

answered Apr 02 '14 at 13:19

thefourtheye

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You are changing the arrays as a side effect – Esailija Apr 02 '14 at 13:52
@Esailija Fixed it :) Please check now. – thefourtheye Apr 02 '14 at 13:55
Sure but why not `return array1.length === array2.length && array1.every(item => array2.indexOf(item) > -1);` much simpler and faster :P – Esailija Apr 02 '14 at 13:57
@Esailija I test the solutions before I post them. That is ES6 and I couldn't test that :( – thefourtheye Apr 02 '14 at 13:57
@Esailija Apart from that, technically that is O(N^2), I believe – thefourtheye Apr 02 '14 at 13:58
Yes but that doesn't mean anything in terms of real performance. I also use arrow function syntax because it's easier to read in a comment. – Esailija Apr 02 '14 at 14:04
@Esailija Oh, got it :) But, if there are duplicate elements in one list and the second list doesn't, this will fail, right? For example, `["a", "a"]` and `["a", "b"]`? – thefourtheye Apr 02 '14 at 14:07
The OP is representing sets as arrays so uniqueness is assumed yes – Esailija Apr 02 '14 at 14:17
@Esailija If the data is guaranteed to be unique, converting the arrays to Objects will be better, right? We get faster lookup. for larger arrays? – thefourtheye Apr 02 '14 at 14:20
@thefourtheye That only works if the items are all strings. I see no reason to believe that is the case. – Aaron Dufour Apr 02 '14 at 14:53
@AaronDufour You are correct, I don't claim that it will work always :) Also OP says `they should come as equal for the above scenario`. This solution was mainly targeted at that statement. – thefourtheye Apr 02 '14 at 14:54

score 0 · Answer 2 · edited Jun 30 '17 at 17:58

0

You can try with _.difference

var diff = _(array1).difference(array2);
if(diff.length > 0) {
    // There is a difference
}

this will not work because different returns diff from first array. _.difference(['a'] ,['a','b']) is 0 but two array is not equal.

edited Jun 30 '17 at 17:58

Aidin A

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answered Apr 02 '14 at 13:31

Fizer Khan

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How do I compare two arrays in nodejs

2 Answers2