CODEWITHSUNDEEP
javascriptarrayscomparison
errata
errata

Reputation: 6041

Comparing two arrays in javascript and creating new arrays with missing and new elements

What is the most efficient way to compare two javascript arrays and create two new arrays of missing and new elements? Array elements will be always strings or numbers and it is not 100% sure that they will be sorted in any way.

var old_array = ['11', '13', '14', '18', '22', '23', '25'];
var new_array = ['11', '13', '15', '16', '17', '23', '25', '31'];
var missing_elements = [];
var new_elements = [];

/*
* some magic goes here
* which compares
* new_array with old_array
*/

console.log(missing_elements); // would produce ['14', '18', '22']
console.log(new_elements); // would produce ['15', '16', '17', '31']

Thanks a bunch!

Upvotes: 2

Views: 1285

Answers (3)

Lukas
Lukas

Reputation: 9845

The code to Drew Noakes' solution:

var old_array = ['11', '13', '14', '18', '22', '23', '25'];
var new_array = ['11', '13', '15', '16', '17', '23', '25', '31'];
var missing_elements = _.difference(old_array, new_array);
var new_elements = _.difference(new_array, old_array);

console.log(missing_elements); // would produce ['14', '18', '22']
console.log(new_elements); // would produce ['15', '16', '17', '31']

Upvotes: 3

Bergi
Bergi

Reputation: 664650

Sorting will be the most efficient (assuming you don't have any other preconditions to base an optimization on):

var old_array_sorted = old_array.slice().sort(); // slicing for not mutating
var new_array_sorted = new_array.slice().sort(); // the original array

for (var o=0, n=0; o<old_array_sorted.length && n<new_array_sorted.length; ) {
    if (old_array_sorted[o] < new_array_sorted[n])
        missing_elements.push ( old_array_sorted[o++] );
    else if (old_array_sorted[o] > new_array_sorted[n])
        new_elements.push( new_array_sorted[n++] );
    else
        n++, o++;
}
[].push.apply(missing_elements, old_array_sorted.slice(o));
[].push.apply(new_elements, new_array_sorted.slice(n));

Upvotes: 0

Drew Noakes
Drew Noakes

Reputation: 311057

I would use Underscore.js's intersection and difference functions.

Upvotes: 2

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