st: RE: Check if variable names are equal for program flow

["Sarah Edgington" <sedging@ucla.edu>]

Eric,
For the if statement you want to put both elements in quotation marks so
that Stata knows you're comparing strings.  Otherwise it will evaluate
whether the value of each of the two variables is equal in the first
observation.
You want the following:
if "`svyitem'" == "smokwholage18_2cat" {


Display isn't evaluating an if statement.  It's just showing you the things
you asked it to display, which is why you get the two strings with no spaces
between them.

Hope that helps.

-Sarah

-----Original Message-----
From: owner-statalist@hsphsun2.harvard.edu
[mailto:owner-statalist@hsphsun2.harvard.edu] On Behalf Of Eric Canen
Sent: Tuesday, September 10, 2013 10:32 AM
To: statalist@hsphsun2.harvard.edu
Subject: st: Check if variable names are equal for program flow

I want to loop over a set of variables using a local macro. There is a
variable in the set where I want to do additional procedures when it comes
up in the loop, so I added an if statement that is meant to compare whether
or not the current variable is the one that has additional procedures. The
problem is that the if statement is not evaluating as I expected. Its
evaluating as true even when as far as I can tell it should be false. Here
is the code:

local cig_init smokever_initiation smokwholcig smokwholage18_2cat
smokwholage18_24

foreach svyitem in `cig_init' {

//do some stuff for every variable
//added the next command to check what the if is evaluating to
display `svyitem' == smokwholage18_2cat if `svyitem' == smokwholage18_2cat{
//do some extra stuff on smokwholage18_2cat { }

The first variable in the loop (smoker_initiation) works fine. The debugging
code using the display command prints a "0" like I expected.
The second variable (smokwholcig) seems to have a problem. The debugging
code prints a "1" and so it is evaluating to true when as far as I can tell
it should be evaluating to a "0" because as far as I can tell smokwholcig
== smokwholage18_2cat is false.

I also tried evaluating the variable names as strings and it just
concatenates them together. Specifically I ran:


. display "`svyitem'" == "smokwholage18_2cat" 

smokwholcigsmokwholage18_2cat


It just concatenated the two strings together.

I have run the frequencies on both variables and they are different from one
another though because of skip patterns in the survey the cross tabulation
does yield a reduced table (see below). That is part of the reason I want to
use the if statement to control what is done for smokwholage18_2cat. Here is
the output of the cross tabulation between the two variables:

. tabulate smokwholcig smokwholage18_2cat

  Have you |

      ever | How old were you when you smoked
  smoked a | a whole cigarette for the first
     whole |         time before 18?
cigarette? |         1          2        997 |     Total
-----------+---------------------------------+----------
         1 |       118        139          7 |       264 
-----------+---------------------------------+----------
     Total |       118        139          7 |       264 

Can anyone help me figure out why this if statement is working the way it is
and what I can do to fix it?

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