How can I look for duplicate values in an array and return True or False?

Question

I've looked all over for an example of this but can't figure it out.

$('.ac-items').on(flexClick, function () {
    var $this = $(this);
    var inputSelection = $this.parent().parent().find('input').val();
    var currentField = $this.parent().parent().find('input');
    var crewInputs = $('input[id^="crew-list-"]');
    var crewChoices = new Array ();
    for (i=0; i<crewInputs.length; i++) {
        crewChoices.push(crewInputs[i].value);
    }
    for (a = 0; a < crewChoices.length; a++) {
        if (inputSelection == crewChoices[a]) {
            alert('try again');
        }

    }

 });

You can use `inArray()` ( http://api.jquery.com/jquery.inarray/ )to test if it is already there. — Daniel, Jan 28 '15 at 23:04
Thorough answer(s) on [similar Stackoverflow question](http://stackoverflow.com/questions/9229645/remove-duplicates-from-javascript-array) — rogMaHall, Jan 28 '15 at 23:07
If you don't want to use jQuery just use indexOf and if the return is -1, the elt is not in the array. — Superdrac, Jan 28 '15 at 23:08
@rogMaHall Thanks for the useful link. It didn't turn up in my query. — NewtonEntropy, Jan 29 '15 at 04:59

score 0 · Answer 1 · answered Jan 28 '15 at 23:08

Test if your value is already in the array. If not, then push it.

    var crewChoices = new Array ();
    for (i=0; i<crewInputs.length; i++) {
        if($.inArray( crewInputs[i].value, crewChoices ) != -1) {
                crewChoices.push(crewInputs[i].value);
        }
    }

score 0 · Answer 2 · answered Jan 28 '15 at 23:10

Are you looking to make a set? JS doesn't have native sets, exactly... but you can get the same functionality (meaning no duplicate items) with objects.

var setObject = {};

var choices = ['foo', 'foo', 'bar', 'baz', 'baz'];

choices.forEach(function(choice){
  setObject[choice] = true;
});

console.log(setObject); // >>> {foo: true, bar: true, baz: true}

How can I look for duplicate values in an array and return True or False?

2 Answers2