How do I reverse an array

Question

Hi I have an array of strings, and I need to output them from the last one to the first one.

I don't see an arrayReverse() function, but I'm only just learning ColdFusion

Answer 1

You can just loop over the array in reverse

<cfloop index="i" from="#arrayLen(myArray)#" to="1" step="-1">
   <cfoutput>#myArray[i]#</cfoutput>
</cfloop>

I think you need to use Java methods to really reverse the array.

<cfscript>
// and for those who use cfscript:
for ( var i = arrayLen( myArray ); i >= 1; i-- ) {
    writeOutput( myArray[i] );
}
</cfscript>

Answer 2

FYI array in CF is just an ArrayList, so...

arr = [1,2,3];
createObject("java", "java.util.Collections").reverse(arr);
writeDump(arr);   // arr becomes [3,2,1]

And I would not bother writing arrayReverse() because array is passed by value in CF (not until CF2016's this.passArraybyReference) so it's super inefficient.

Answer 3

I wrote this function to reverse an array. It modifies the array and returns it.

function init(required array arr) {
    var arrLen = arrayLen(arr);
    for (var i = 1; i <= (arrLen / 2); i++) {
        var swap = arr[arrLen + 1 - i];
        arr[arrLen + 1 - i] = arr[i];
        arr[i] = swap;
    }
    return arr;
}

I've tested it, and it works on arrays of strings, as well as objects, etc.

writeOutput(arrayReverse(['a','b','c']) ); // => ['c', 'b', 'a']

var a = ['apple', 'ball', 'cat', 'dog'];
arrayReverse(a);
writeOutput(a); // => ['dog', 'cat', 'ball', 'apple']

I put it into it's own component, so it's easier to use in different projects.

Answer 4

Oh but there is an ArraySort method!

ArraySort( array, sort_type [, sort_order] );

Returns boolean.

array is updated by reference.

sort_type can be numeric, text or textnocase

sort_order can be asc or desc

<cfscript>
test = [ "c", "d", "a", "b" ];
arraySort( test, 'textnocase' );

test is now:
[ "a", "b", "c", "d" ]

</cfscript>

Check out the documentation here:

https://helpx.adobe.com/coldfusion/cfml-reference/coldfusion-functions/functions-a-b/arraysort.html