Knowing when to insert a comma in ColdFusion

Question

Every so often, either in display code or in assembling a string, I'll be making a list and need to figure out how to insert commas in that list.

This is how I usually do it:

<cfset hide_comma=true>
<cfloop ... some kind of loop ...>
    <cfif hide_comma><cfset hide_comma=false><cfelse>,</cfif>
    .... rest of code here ...
</cfloop>

I'm wondering if there's a cleaner way of doing this. I realize one option would be something like the following:

<cfset output_as_array = []>
<cfloop ... some kind of loop ...>
    <cfset loop_output = "">
    ... rest of code here, but append all output to loop output instead ...
    <cfset ArrayAppend(output_as_array, trim(loop_output))>
</cfloop>
<cfoutput>#ArrayToList(output_as_array, ", ")#</cfoutput>

But that doesn't really seem any clearer.

In Django, in contrast, each loop has a built in counter so I can write something like:

{% for ... some kind of loop ... %}
    {% if not forloop.first %},{% endif %}
    ... rest of code here ...
{% endfor %}

Pretty much the same logic, only there's already a built-in way to check loop state, rather than having to create one on my own. I know that when looping through a <cfoutput query=...> I can use QueryName.RowCount for this purpose, but can't find anything similar in the documentation for CFLOOPs.

Answer 1

For compiling a variable, using the ValueList (for queries) and ArrayToList functions is a sensible approach.

If not dealing with a query or array, build an array using ArrayAppend then convert to string with ArrayToList.

(Note: ListAppend is ok for one or two items, but in a long loop it's slower than using ArrayAppend+ArrayToList - see info here.)

Regarding:

Pretty much the same logic, only there's already a built-in way to check loop state, rather than having to create one on my own. I know that when looping through a I can use QueryName.RowCount for this purpose, but can't find anything similar in the documentation for CFLOOPs.

Short answer: no, there isn't a built-in automatic index for loops in ColdFusion, other than standard from/to and query loops.

For index loops, you can of course use the index:

<cfloop index="Index" from=1 to=#ArrayLen(MyArray)#>
    <cfif Index GT 1> Not First Row </cfif>
</cfloop>

For query loops, use rowcount:

<cfloop query="MyQuery">
    <cfif MyQuery.RowCount GT 1> Not First Row </cfif>
</cfloop>

For looping through items, you need to create your own variable:

<cfset Row = 0 />
<cfloop index="Item" array=#MyArray#>
    <cfif ++Row GT 1> Not First Row </cfif>
</cfloop>

<cfset Row= 0 />
<cfloop item="Item" collection=#MyStruct# >
    <cfif ++Row GT 1> Not First Row </cfif>
</cfloop>

In Railo, you can specify both index and item attributes and have both values available:

<cfloop index="Index" item="Item" array=#MyArray#>
    <cfif Index GT 1> Not First Row </cfif>
</cfloop>

The index refers to the key though, so you cannot do that with structs (you'll get the key name, not row number).

Answer 2

You can use ListAppend()

Sample code:

<cfset myList = "" />
<cfloop ....>
    <cfset myList = listAppend( myList, 'some value') />
</cfloop>

This will give you a comma delimited list. If you want/need to list delimited by another character, you can specify that as a second argument in listAppend()

I just ran a test here - and it seems that using arrayAppend() then arrayToList() is much faster than using listAppend(). So the code using array append should be the best path to take.

Answer 3

I like to do something like this:

<cfset separator="">
<cfloop ...>
  #variables.separator#
  <!--- rest of code here --->
  <cfset separator=", ">
</cfloop>