What is the fastest way to copy an array? Concat or Slice? There is only one way to find out. FIGHT!
OK, so we can dismiss any kind of for-loop – far too slow, so that leaves us with:
1) array.concat() – i.e. concatenate an array onto nothing and deliver that as a new array.
2) array.slice(0) – i.e. return a new array consisting of all of the elements of the old array – from 0 till the end (up to a max of 16777215)
I’ve set up an array with a cool 1million entries (ok, it is not big, and it is not clever so it certainly isn’t cool). I need to copy this. The following code executes each method once on every iteration. It keeps a running total and records the average time each takes. I’ve limited the code to 100 iterations.
import flash.utils.*;
var iteration_count:int=0
var concat_total:int=0
var slice_total:int=0//Set up array to copy
var test_array:Array = [];
for(var i:int = 0; i < 1000000; i++) test_array.push(i);addEventListener(Event.ENTER_FRAME,iterate)
function iterate(e:Event=null):void
{
concat_total+=testConcat()
slice_total+=testSlice()
iteration_count++
trace(“Av. concat time=”+(concat_total/iteration_count)+” Av. slice time=”+(slice_total/iteration_count))
if(iteration_count>99) removeEventListener(Event.ENTER_FRAME,iterate)
}//test array slice
function testSlice():int
{
var time_slice_start:Number = getTimer();
var slice_copy:Array = test_array.slice(0);
var time_slice_end:Number = getTimer();
return time_slice_end-time_slice_start
}//test array concat
function testConcat():int
{
var time_concat_start:Number = getTimer();
var concat_copy:Array = test_array.concat();
var time_concat_end:Number = getTimer();
return time_concat_end-time_concat_start
}
On my laptop I’m clocking the concat at 14ms and the slice at over 29ms.
So a conclusive result. concat is twice the speed (with large arrays – the difference diminishes considerably with smaller arrays)
Thinking about it the may be some issues with memory usage and garbage collection that could affect the test.
Give the code a few run throughs and see what you get. Let me know if your results are markedly different.
