st: Use of local macros when generating new variables (-rowranks-)

[Michael Crain <michaelcrain@ymail.com>]

Using Nick Cox's -rowranks- ado that ranks values across rows, the
general syntax is:
rowranks x1-x5, generate(r1-r5)

My very large dataset consists of subsets of rows (variables) that I
want to rank. I need some help on the syntax (or approach).

My variables have this general form: C[code string]_[time period]

I want to rank across the C[code string] variables by _year_. For
instance, my variables look like this:

Cabc_1
Cdef_1
C456_1
C789_1
Cabc_2
Cdef_2
C456_2
C789_2
Cabc_3
Cdef_3
C456_3
C789_3

I want to rank across Cabc Cdef C456 C789 for each time period so:
a. rank across Cabc_1 Cdef_1 C456_1 C789_1, then
b. rank across Cabc_2 Cdef_2 C456_2 C789_2, then 
c. rank across Cabc_3 Cdef_3 C456_3 C789_3

I tried using a loop but my problem is how to write the -rowranks-
syntax for the subset variable range for the source variables and new
rank variables.

My loop is this:

levelsof timedummy, local(timeperiod)
levelsof codestring, local(code)
foreach t of local timeperiod {
   foreach c of local code {
      rowranks C`c'_`t', gen(R`c'_`t')
      }
   }

With this code, Stata sees my source variables (over 200 of them in year time period), but sees only one new variable name (an error). I tried variations of this syntax for the variables with no success,

Can anyone help with the syntax? Or is there is a better approach?

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