st: re: cond(a,b,c) fn

[Kit Baum <baum@bc.edu>]

James writes

When I use the cond(x,a,b,c) function, I could not generate the value c
when x is missing. For example:

sysuse auto, clear
tab rep78, mi
gen a=cond(rep78==1, 1, 0, .)
tab a, mi

It gives

a	Freq.	Percent	Cum.
			
0	72	97.30	97.30
1	2	2.70	100.00
			
Total	74	100.00

There should be 5 missing values for variable a according to the manual.
Thanks for your input.



The online help says

 cond(x,a,b,c) returns a if x evaluates to true (not 0), b if x 
evaluates to false
        (0), and c if x evaluates to missing (.).

Since "rep78==1" never evaluates to missing, a will never be set to 
missing.
A way to achieve this is

. g a = (rep78==1)*rep78/rep78

. tab a,mi

          a |      Freq.     Percent        Cum.
------------+-----------------------------------
          0 |         67       90.54       90.54
          1 |          2        2.70       93.24
          . |          5        6.76      100.00
------------+-----------------------------------
      Total |         74      100.00

Kit Baum, Boston College Economics
http://ideas.repec.org/e/pba1.html

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