Compare 2 arrays and show unmatched elements from array 1 [duplicate]

Question

I have 2 arrays as follows. I want to compare both arrays and only provide the elements from 'check' which are not present in 'data' array.

var check= ["044", "451"],
data = ["343", "333", "044", "123", "444", "555"];

The function used is as follows. This function will result in providing the elements in 'check' array which are present in 'data' array

function getMatch(a, b) {
var matches = [];

for ( var i = 0; i < a.length; i++ ) {
    for ( var e = 0; e < b.length; e++ ) {
        if ( a[i] === b[e] ) matches.push( a[i] );
    }
}
return matches;
}

getMatch(check, data); // ["044"] ---> this will be the answer as '044' is only present in 'data'

I want to have a list of elements which are not present in 'data' array. Can someone let me know how to achieve this.

Answer 1

You could use filter and Set, providing the Set as context to the filter method, so it can be accessed as this:

var check= ["044", "451"],
data = ["343", "333", "044", "123", "444", "555"];

var res = check.filter( function(n) { return !this.has(n) }, new Set(data) );

console.log(res);

Note that this runs in O(n) time, contrary to indexOf/includes based solutions, which really represent a nested loop.