st: Re: Accessing the number of changes made by a "replace" command

["Michael Blasnik" <michael.blasnik@verizon.net>]

Although you can solve this problem by using a count statement immediately 
before the replace command to test how many will be replaced, I still wish 
that Stata would make the number of changes  available to the user.  In a 
very large dataset, the extra time required just for the added count command 
can add up, especially in a loop that may execute many times through.  For 
example, when I need to clean up text variables that may have multiple 
consecutive embedded spaces (sometimes up to 20 or 30 spaces may be padded 
inside a string) and I want no more than one space, I need to do this:

count if index(name,"  ")
while r(N)>0 {
replace name=subinstr(name,"  "," ",.)
count if index(name,"  ")
}

On a dataset with 1,000,000 observations and a string variable that may 
require 10-20 passes through this loop and perhaps several of these string 
variables, the time required for the count statements can become 
non-trivial.  Although it isn't a tremendous amount of time, it seems like 
purely wasted time since the information needed to avoid the count statement 
is printed right on the screen.

I would think that it wouldn't be too difficult to have the replace command 
put the number of changes in someplace like s(changes).

Michael Blasnik
michael.blasnik@verizon.net

----- Original Message ----- 
From: "David Fisher" <djfisher81@msn.com>
To: <statalist@hsphsun2.harvard.edu>
Sent: Friday, March 18, 2005 5:03 AM
Subject: st: Accessing the number of changes made by a "replace" command



> Hi all,
> I am attempting to create a "while" loop that executes, amongst other 
> things, a "replace" command on a particular variable.  I would like this 
> loop to continue until the "replace" command cannot make any more changes 
> to the data.  In order to do this I would like to be able to access the 
> number of (real) changes made by the "replace" command, so that I can say 
> something like "loop while (number of real changes)!=0".  Is there a way 
> to do this in Stata?  I thought there might be an underscore variable that 
> would do this, but I can't find one.
> Thanks!
> David Fisher.
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