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Re: st: if command


From   David Kantor <dkantor@jhu.edu>
To   statalist@hsphsun2.harvard.edu
Subject   Re: st: if command
Date   Thu, 12 Feb 2004 17:02:47 -0500

At 03:26 PM 2/12/2004 -0500, Danielle Ferry wrote:

Can anyone please explain when the if command requires quotes around the expression and when it does not?

For example, I've found the following seemingly quirky behavior:

1) if "`1'"=="aRate" | "`1'"=="bRate" | "`1'"=="pRate" --> requires quotes
2) if `1'==aRate --> does not require quotes
3) if "`1'"=="apRatio" --> requires quotes
As far as I know, if you are comparing to a string constant, you need quotes.

Example 2 probably ought to have quotes if it is meant to test a string value. It would, however, pass as a legitimate expression if...
aRate happens to be a variable name and...
it is numeric and so is `1' (that is the contents of the local 1), or
it is string, and `1' contains enclosing quotes (I haven't tried this), or
it is either numeric or string, and `i' is also a variable name of a compatible type.
But in these cases, you are implicitly testing observation 1, which you might not have intended.

Example 2 would also pass if aRate is a scalar and `1' is numeric (and if `1' is a variable name, then you are testing observation 1).

In any case, while Example 2 might sometimes pass, it is probably not doing what you intended.

I hope this helps.
-- David

David Kantor
Institute for Policy Studies
Johns Hopkins University
dkantor@jhu.edu
410-516-5404

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