Best way to join arrays in Actionscript

Question

I need to add one array to another (only care about saving the joined one). Which is the preferred way of doing this? Speed is the primary concern followed by readability (I consider Option 1 to be a cleaner option). I assume it might also depend on the length of the arrays, but are there any good guidelines?

Option 1:

var array1:Array = new Array("1","2","3");
var array2:Array = new Array("4","5","6");

// Don't care about array2 after this point.
var array1 = array1.concat(array2);

Option 2:

var array1:Array = new Array("1","2","3");
var array2:Array = new Array("4","5","6");

// Don't care about array2 after this loop has run.
for each(var item:Object in array2)
{
    array1.push(item);
}

sberry · Accepted Answer · 2011-01-13 21:32:14Z

This sounds like a job for... benchmark!

import flash.utils.getTimer;

function addItems($array:Array, $start:int, $count:int) {
    for (var i:Number = $start; i < $start + $count; i++) {
        $array.push(i);
    }
}

function concatArrays($array1:Array, $array2:Array):Number {
    var t1:Number = getTimer();
    $array1.concat($array2);
    var t2:Number = getTimer();
    return t2 - t1;
}

function pushArrays($array1:Array, $array2:Array):Number {
    var t1:Number = getTimer();
    for each (var item:Object in $array2) {
        $array1.push(item);
    }
    var t2:Number = getTimer();
    return t2 - t1;
}

function testBed() {
    for (var i:Number = 10000; i <= 100000; i+=10000) {
        trace("\n---- New test");
        var a1:Array = [];
        var a2:Array = [];
        addItems(a1, 0, i);
        addItems(a2, i, i);
        trace("For " + a1.length + " items: ");
        trace("concatArrays: " + concatArrays(a1, a2));
        trace("pushArrays:   " + pushArrays(a1, a2));
    }
}

testBed();

As I would have suspected, concat is far faster, especially when dealing with larger arrays.

OUTPUT

---- New test
For 10000 items: 
concatArrays: 1
pushArrays:   1

---- New test
For 20000 items: 
concatArrays: 1
pushArrays:   4

---- New test
For 30000 items: 
concatArrays: 1
pushArrays:   4

---- New test
For 40000 items: 
concatArrays: 2
pushArrays:   5

---- New test
For 50000 items: 
concatArrays: 1
pushArrays:   6

---- New test
For 60000 items: 
concatArrays: 1
pushArrays:   7

---- New test
For 70000 items: 
concatArrays: 1
pushArrays:   8

---- New test
For 80000 items: 
concatArrays: 2
pushArrays:   12

---- New test
For 90000 items: 
concatArrays: 2
pushArrays:   13

---- New test
For 100000 items: 
concatArrays: 3
pushArrays:   14

Those numbers are in milliseconds, so as Richard points out, unless your arrays have a huge number of elements, or you are concatenating arrays very frequently, then this is an optimization that is not worth your time

Thanks for taking the time to put this together! I know micro-optimization is pointless, but I still get bothered when I don't know the answer to a question like this, haha.

Richard Szalay · Accepted Answer · 2011-01-13 21:15:40Z

4

I would use concat personally, because it's simpler.

It's probably faster, too (because it can be natively implemented), but measure it if it's important to you. Unless you are dealing with an extremely large number of array values, there's unlikely to be a difference and would be a prime example of micro-optimisation.

answered Jan 13, 2011 at 21:15

Richard Szalay

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