Get some set of array based on condition from two arrays of array in Javascript

Question

I have two arrays of array in Javascript like

var array1 = [[10, 2], [11, 4], [12, 30], [13, 17], [14, 28]];
var array2 = [[8, 13], [9, 19], [10, 6], [11, 7], [12, 1]];

I want to get the set of arrays from array1 which match the first element of each array of the array2

in my example case both array1 and array2 have array with first element as 10 11 and 12, so it should return

[[10, 2], [11, 4], [12, 30]];

is there any easy and efficient way using pure javscript or lodash, underscor framework or something like that. Without iterate over and match one by one of this two array ?

Answer 1

In ES6, you could use Set.

var array1 = [[10, 2], [11, 4], [12, 30], [13, 17], [14, 28]],
    array2 = [[8, 13], [9, 19], [10, 6], [11, 7], [12, 1]],
    set = new Set(array2.map(a => a[0])),
    result = array1.filter(a => set.has(a[0]));

console.log(result);

Version with an object as hash table

var array1 = [[10, 2], [11, 4], [12, 30], [13, 17], [14, 28]],
    array2 = [[8, 13], [9, 19], [10, 6], [11, 7], [12, 1]],
    result = array1.filter(function (a) {
        return this[a[0]];
    }, array2.reduce(function (r, a) { 
        r[a[0]] = true;
        return r;
    }, Object.create(null)));

console.log(result);

Answer 2

You can use lodash _.intersectWith function in order to solve this problem in an inline.

_.intersectionWith(array1, array2, function(a, b) {
    return a[0] === b[0];
});

I don't know about performance cos I haven't had the chance to have a look at the source code of this function. Anyway, I like it for its simplicity. Here's the fiddle in case you want to check it out.