In my daily blog reading I came across Mr. Ray Camden’s blog post about rotating a grouped set of data in a “round robin” fashion. In his example he uses a multi-dimensional array, then uses ColdFusion to iterate over the array, copy the item to move, delete it, them push it to the end of the array, thus “rotating” it. That looks like this.
<cfloop index="i" from="1" to="#arrayLen(data)#">
<cfset movingItem = data[i][1]>
<cfset arrayDeleteAt(data[i],1)>
<cfset arrayAppend(data[i], movingItem)>
</cfloop>Being the giant nerd that I am I wanted to see if we could do this using the big Java-Hemi under the hood of ColdFusion. Sure enough, the Java Collections class has a way to do this! Built right in! I’m not going to go into the setup, because Mr. Camden took care of that already (go read it), but I will show you that we use the rotate method on the Collections class. And in his example it is an array of arrays, so we will loop over the first level of the array, and apply the rotate method to each sub-array.
<cfloop from="1" to="#arrayLen(data)#" index="i">
<cfset collection.rotate(data[i], -1) />
</cfloop>Super cool eh? Here is the code sample in full. Happy coding, and thanks for the interesting blog post Ray!
<cffunction name="render" returntype="void" access="public" output="true">
<cfargument name="arr" type="array" required="true" />
<cfset var i = 0 />
<cfset var x = 0 />
<cfloop array="#arguments.arr#" index="i">
<cfloop array="#i#" index="x">
<cfset writeOutput("#x# ") />
</cfloop>
</cfloop>
<cfset writeOutput("
") />
</cffunction>
<cfset collection = createObject("java", "java.util.Collections") />
<cfset data = [
["a", "b", "c"],
["d", "e"]
] />
<!---
Display the original data array
--->
<cfset render(data) />
<!---
Rotate the arrays
--->
<cfloop from="1" to="#arrayLen(data)#" index="i">
<cfset collection.rotate(data[i], -1) />
</cfloop>
<cfset render(data) />
<!---
Rotate the arrays... again
--->
<cfloop from="1" to="#arrayLen(data)#" index="i">
<cfset collection.rotate(data[i], -1) />
</cfloop>
<cfset render(data) />