What do you all think would be the best (best can be interpreted as most readable or most performant, your choice) way to write a function using the lodash utilities in order to check an array for duplicate values.
I want to input ['foo', 'foo', 'bar'] and have the function return true. And input ['foo', 'bar', 'baz'] and have the function return false.
You can try this code:
function hasDuplicates(a) { return _.uniq(a).length !== a.length; } var a = [1,2,1,3,4,5]; var b = [1,2,3,4,5,6]; document.write(hasDuplicates(a), ',',hasDuplicates(b));You could check that there is _.some element in the array which does not return its own location when looked up in the array. In other words, there is at least one element which has a match earlier in the array.
function hasDuplicates(array) { return _.some(array, function(elt, index) { return array.indexOf(elt) !== index; }); } Perhaps this is faster than the _.uniq solution, since it will identify the first duplicated element right away without having to compute the entire unique-ified array.
Or, depending on your coding style and desire for readability, and if you want to use ES6 arrow functions for brevity:
var earlierMatch = (elt, index, array) => array.indexOf(elt) !== index; var hasDuplicates = array => _.some(array, earlierMatch); Well, there's always. lodash's _.uniq() function. That function actually returns a new array that only contains unique values, so checking to see if the length of the array has changed would get you your 'true' or 'false' value to return yourself, I believe.
I don't know lodash but I submit:
_.any(_.countBy(['foo', 'foo', 'bar']), function(x){ return x > 1; }); The problem with all the solutions proposed so far is that the entire input array needs processing to get an answer, even if the answer is obvious from the first 2 elements of the array.