Cleanly merge two arrays in ActionScript (3.0)?

Question

What's a nice way to merge two sorted arrays in ActionScript (specifically ActionScript 3.0)? The resulting array should be sorted and without duplicates.

Answer 1

To merge (concatenate) arrays, use .concat().

Below are two examples of how you can concatenate arrays and remove duplicates at the same time.

More convenient way: (you can use ArrayUtil.createUniqueCopy() from as3corelib)

// from as3corelib:
import com.adobe.utils.ArrayUtil;

var a1:Array = ["a", "b", "c"];
var a2:Array = ["c", "b", "x", "y"];

var c:Array = ArrayUtil.createUniqueCopy(a1.concat(a2)); // result: ["a", "b", "c", "x", "y"]

Slightly faster way: (you can loop through the arrays yourself and use Array.indexOf() to check for duplicates)

var a1:Array = ["a", "b", "c"];
var a2:Array = ["c", "b", "x", "y"];
var a3:Array = ["a", "x", "x", "y", "z"];

var c:Array = arrConcatUnique(a1, a2, a3); // result: ["a", "b", "c", "x", "y", "z"]

private function arrConcatUnique(...args):Array
{
    var retArr:Array = new Array();
    for each (var arg:* in args)
    {
        if (arg is Array)
        {
            for each (var value:* in arg)
            {
                if (retArr.indexOf(value) == -1)
                    retArr.push(value);
            }
        }
    }
    return retArr;
}

Answer 2

This is kind of an simple algorithm to write. I would be surprised if there were a more direct way to do this in Actionscript.

function merge(a1:Array, a2:Array):Array {
    var result:Array = [];
    var i1:int = 0, i2:int = 0;

    while (i1 < a1.length && i2 < a2.length) {
        if (a1[i1] < a2[i2]) {
            result.push(a1[i1]);
            i1++;
        } else if (a2[i2] < a1[i1]) {
            result.push(a2[i2]);
            i2++;
        } else {
            result.push(a1[i1]);
            i1++;
            i2++;
        }
    }

    while (i1 < a1.length) result.push(a1[i1++]);
    while (i2 < a2.length) result.push(a2[i2++]);

    return result;
}

Answer 3

Using Array.indexOf to detect duplicates is going to be painfully slow if you have a List containing a large number of elements; a far quicker way of removing duplciates would be to throw the contents of the Array into a Set after concatenating them.

// Combine the two Arrays.
const combined : Array = a.concat(b);

// Convert them to a Set; this will knock out all duplicates.
const set : Object = {};  // use a Dictionary if combined contains complex types.

const len : uint = combined.length;
for (var i : uint = 0; i < len; i++) {
    set[combined[i]] = true;
}

// Extract all values from the Set to produce the final result.
const result : Array = [];
for (var prop : * in set) {
    result.push[prop];
}

If your program makes heavy use of Collections then if may be prudent to make use of one of the many AS3 Collections frameworks out there which provide a simple interface for manipulating data and will always take the optimal approach when it comes to the implementation.

• AS3Commons Collections
• Polygonal DS

Answer 4

function remDuplicates(_array:Array):void{
    for (var i:int = 0; i < _array.length;++i) {
        var index:int = _array.indexOf(_array[i]);
        if (index != -1 && index != i) {
            _array.splice(i--, 1);
        }
    }
}

Then for the "merge" use concat. exemple :

var testArray:Array = [1, 1, 1, 5, 4, 5, 5, 4, 7, 2, 3, 3, 6, 5, 8, 5, 4, 2, 4, 5, 1, 2, 3, 65, 5, 5, 5, 5, 8, 4, 7];
var testArray2:Array = [1, 1, 1, 5, 4, 5, 5, 4, 7, 2, 3, 3, 6, 5, 8, 5, 4, 2, 4, 5, 1, 2, 3, 65, 5, 5, 5, 5, 8, 4, 7];

testArray.concat(testArray2);
trace(testArray);
remDuplicates(testArray);
trace(testArray);