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

This expression gives you all the unique elements in the array without mutating it:

arr.filter(function(v,i) { return i==arr.lastIndexOf(v); })

You can chain it with this expression to build your string of results without sorting:

.forEach(function(v) {
     results+=v+" --> " + arr.filter(function(w){return w==v;}).length + " times\n";
});

In the first case the filter takes only includes the last of each specific element; in the second case the filter includes all the elements of that type, and .length gives the count.