Count unique elements in array without sorting

Question

In JavaScript the following will find the number of elements in the array. Assuming there to be a minimum of one element in the array

arr = [\"jam\", \"beef\         


        

Answer 1

Why not something like:

var arr = ["jam", "beef", "cream", "jam"]
var uniqs = arr.reduce((acc, val) => {
  acc[val] = acc[val] === undefined ? 1 : acc[val] += 1;
  return acc;
}, {});
console.log(uniqs)

Pure Javascript, runs in O(n). Doesn't consume much space either unless your number of unique values equals number of elements (all the elements are unique).