Help manipulate a string

This is a question related to :  

https://www.experts-exchange.com/questions/27644050/Help-manipulating-a-String.html


the problem is if the string looks up first the second part of the string in the list

sbKeys will be inverted

for example:

lets say the list is :

Per1, Period 1
TY, This Year
LY, Last Year
Q1, This is Q1
Q2, This is Q2


and string is:   "This Year Period 1'

sbKeys will be:   "Per1_TY"

but the real result would need to be:  "TY_Per1"
like if it must be from left to right..

how could we modify the code ?