Re: st: combine foreach and if

[Vincent Koppelmans <vkoppel@umich.edu>]

Dear Nick,

Thank you for your prompt reply.

One of the problems is that there are some commands in the syntax that do not seem to work with the if option at the end of the line (e.g. estpost).

However, I created the following workaround:


save "/Path/outfile.dta"

foreach TIME of numlist 1, 5 {
clear
use "/Path/outfile.dta"
drop if time ~= `TIME'
summ DS_sec_
plot DS_sec_ Subject_ID
}


best,

Vincent


Op 4 mrt. 2014, om 15:13 heeft Nick Cox <njcoxstata@gmail.com> het volgende geschreven:

I think you are confusing the -if- command and the -if- qualifier. The
key point is that two code segments are in no sense alternatives, as

if time == `TIME' {
}


will always be interpreted as

if time[1] == `TIME' {
}

which is evidently not what you want. This is documented at

FAQ     . . . . . . . . . . . . . . . . . . . . if command versus if qualifier
       . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .  J. Wernow
       4/05    I have an if or while command in my program that
               only seems to evaluate the first observation.
               What's going on?
               http://www.stata.com/support/faqs/programming/
               if-command-versus-if-qualifier/


Otherwise put, your stylistic preferences collide with Stata's syntax
rules and that's an unequal contest.

In any case I don't understand quite what is your objection to the
second form. If you have other code to be carried out for all data
points, then quite simply it doesn't belong in the -foreach- block.

You will probably need to say more about what you want to do in the
rest of the code to get better advice.

Nick
njcoxstata@gmail.com


On 4 March 2014 20:02, Vincent Koppelmans <vkoppel@umich.edu> wrote:

I want to loop over a couple of time points in a dataset and filer out certain rows.
I tried to combine a foreach loop with an if statement, but it is not working (it only prints the results using the first value of the numlist):


foreach TIME of numlist 1 5 {
if time == `TIME' {
summ DS_sec_
plot DS_sec_ Subject_ID
}
}


The following code however is working:

foreach TIME of numlist 1 5 {
summ DS_sec_ if time == `TIME'
plot DS_sec_ Subject_ID if time == `TIME'
}

In this simple example the syntax does not differ a lot in length, but the actual code that needs to be executed is much longer. I therefore would prefer a solution that resembles my initial code, because that would mean that I do not have to add the "if time == `TIME'" part after each line.

How can I do this?


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