how to replace values using a loop in Nifi

[#1]

I have an attribute which contains a list and I want to replace values with an incrementing value.

Examlple:

Input-

Variable1 = a,b,c

Output-

Variable1=$1a,$2b,$3c

I'm able to count the number of value in the attribute using :

${allDelineatedValues(${col_name}, ","):count()}

After getting the count I want to place as many $1,$2,$3......so on till it reaches the count. How can I do it?

Thanks

[#2]

@Matt Burgess @Timothy Spann @Matt Clarke

[#3]

For this I have used a python script to do the job but I wonder if it can be done with nifi expression langauge.