Question

Being fairly new to Stata, I’m having a difficulty figuring out how to do the following:

I have time-series data on selling price (p) and quantity sold (q) for 10 products in a single datafile (i,e., 20 variables, p01-p10 and q01-q10). I am strugling with appropriate stata command that computes sales revenue (pq) time-series for each of these 10 products (i.e., pq01-pq10).

Many thanks for your help.

Answer 1

forval i = 1/10 { 
      local j : display %02.0f `i' 
      gen pq`j' = p`j' * q`j' 
}

A standard loop over 1/10 won’t get you the leading zero in 01/09. For that we need to use an appropriate format. See also

@article {pr0051,
author = “Cox, N. J.”,
title = “Stata tip 85: Looping over nonintegers”,
journal = “Stata Journal”,
publisher = “Stata Press”,
address = “College Station, TX”,
volume = “10”,
number = “1”,
year = “2010”,
pages = “160-163(4)”,
url = “http://www.stata-journal.com/article.html?article=pr0051”
}

(added later) Another way to do it is

local j = string(`i', "%02.0f") 

That makes it a bit more explicit that you are mapping from numbers 1,…,10 to strings “01”,…,”10″.