Javascript for..in vs for loop performance

Question

I was clustering around 40000 points using kmean algorithm. In the first version of the program I wrote the euclidean distance function like this

var euclide         


        

Answer 1

As a side note, if you cache the length of p1:

var plen = p1.length;
for( var i = 0; i < plen; i++ )

you will get a slight speed increase.

...And if you memoize the function, it will cache results, so if the user tries the same numbers you will see a massive speed increase.

var eDistance = memoize(euclideanDistance);  

function memoize( fn ) {  
    return function () {  
        var args = Array.prototype.slice.call(arguments),  
            hash = "",  
            i = args.length;  
        currentArg = null;  
        while (i--) {  
            currentArg = args[i];  
            hash += (currentArg === Object(currentArg)) ?  
            JSON.stringify(currentArg) : currentArg;  
            fn.memoize || (fn.memoize = {});  
        }  
        return (hash in fn.memoize) ? fn.memoize[hash] :  
        fn.memoize[hash] = fn.apply(this, args);  
    };  
}

eDistance([1,2,3],[1,2,3]);
eDistance([1,2,3],[1,2,3]); //Returns cached value

credit: http://addyosmani.com/blog/faster-javascript-memoization/