Dear all,
I have found the a problem, which, not surprisingly, I have no idea why it
happens. I am using Stata 9.2 SE (Windows XP emulated in Fedora).
Concisely, I wish to run a loop, compute a statistic, and store the
results in my current dataset. In this respect, the problem relies on the
fact that some observations of the statistic of interest are not
computed/stored.
For example, suppose I want to compute a P value from an exact test. Let�s
consider the exact p value obtained by -genwhi-, a program used in
Genetics.
----- Example 1 ---------------
clear
local example 10
set obs `example'
gene a = round(uniform()*25)
gene b = round(uniform()*25)
gene c = round(uniform()*25)
qui gene p_example=.
forvalues i = 1/`example' {
qui genhwi `=a[`i']' `=b[`i']' `=c[`i']'
qui replace p_example = r(p_exact) in `i'
}
---- End Example 1 -----------
Using the example just described above, I successfully get all results
without problems. Nevertheless, if I increase the number of observations,
say, local example 1000, then several observations are not
computed/stored. For example:
a b c p_example
15 7 4 .5175038
7 11 3 .
23 20 18 .
8 10 22 .
0 20 20 .0000885
17 23 1 .0132223
10 12 15 1
.
.
.
6 2 20
16 16 12 .0000974
4 17 16
7 2 8 .4895405
Interestingly enough, this also happens when all observations are equal,
that is:
----- Example 2 ---------------
clear
local example 1000
set obs `example'
gene a = 25
gene b = 50
gene c = 25
qui gene p_example=.
forvalues i = 1/`example' {
qui genhwi `=a[`i']' `=b[`i']' `=c[`i']'
qui replace p_example = r(p_exact) in `i'
}
---- End Example 2 -----------
which gives:
a b c p_example
25 50 25 .
25 50 25 1
25 50 25 .
25 50 25 1
25 50 25 1
25 50 25 1
25 50 25 .
25 50 25 1
.
.
.
25 50 25 .
25 50 25 1
25 50 25 .
I do not have Stata 10 in my home PC, but will try to investigate if the
same problem occurs in that version of Stata. If you have any tip and/or
suggestions, I will be, as usual, appreciating your time and help.
Regards,
Tiago
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