Re: st: Generating a binary variable

[Phil Schumm <pschumm@uchicago.edu>]

On Apr 1, 2010, at 10:54 PM, Nik Pineider wrote:
> I'm having trouble getting this to generate. gen ecobuy = 1 if  
> ecolbs > 0 & ecobuy = 0 if ecolbs = 0. What am I doing wrong here?


If ecolbs is nonnegative and never missing, then you can use

    assert 0 <= ecolbs & !mi(ecolbs)
    gen ecobuy = (0 < ecolbs)

where the first line simply verifies the assumption (for safety and  
readability).  If, however, ecolbs has missing and/or negative values,  
then you need to decide what value(s) ecobuy should take in those  
cases.  For example, your original code (suitably broken onto two  
lines, as suggested by others) would result in ecobuy == 1 if ecolbs  
is missing, and ecobuy == . if ecolbs is negative.  You can achieve  
the same thing by modifying the line above with an -if- condition:

    gen ecobuy = (0 < ecolbs) if 0 <= ecolbs

Note that this is probably *not* what you want (since it will set  
ecobuy = 1 if ecolbs is missing).  Instead, you probably want

    gen ecobuy = (0 < ecolbs) if 0 <= ecolbs & !mi(ecolbs)

which will set ecobuy to missing if ecolbs is negative or missing.

If any of this is unclear, you should read [U] 13 Functions and  
expressions (especially 13.1 and 13.2) and [U] 12.2.1 Missing values.


-- Phil

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