The fastest way to get the number of unique elements in a javascript array

Question

I need to find the number of unique elements in an array.

var myArray = [ 10, 10, 20, 20, 30, 30, 40, 40, 40, 40, 50, 50, 50, 50, 60 ]; 

I want count = 6 (the number of unique elements in the array)

And is there a way to do this without iterating through an array? (I guess this would be the fastest way?).

ANSWER: I used the .filter method as shown below. My actual array element is much more complicated. I finished the iteration through my array and created a new array. Each element of the new array was a .substr of the old element. Then the .filter method below worked fine. THANKS to everyone!

Answer 1

You need to save a set of known values ​​and an auxiliary account. You can use .reduce() :

 var count = myArray.reduce(function(values, v) { if (!values.set[v]) { values.set[v] = 1; values.count++; } return values; }, { set: {}, count: 0 }).count; 

Starting with an empty set of values ​​and a zero count, it looks at each element to see if it is added to the set. If this is not the case, it is added and the score is increased.

Answer 2

How about filter and length:

 var len = myArray.filter(function(val, i, arr) { return arr.indexOf(val) === i; }).length; 

Answer 3

If you are using lodash:

 _.uniq(myArray).length 

Answer 4

ES6 offers a single-line solution:

 Array.from(new Set(myArray)).length