Loop in another loop

[Saleh Babazadeh]

Hi I am trying to make a loop inside another loop but it does not work. What's wrong with my code?

foreach var of varlist stock_implants stock_iud stock_sayana_press stock_depo_provera stock_pills stock_male_condoms stock_female_condoms stock_ec stock_diaphragm stock_foam stock_beads stock_injectable {

gen no_`var'=1 if `var'>1 & `var'<.

   foreach x of varlist no_`var'{
   
recode no_`var' (.=0) if fp_offered=1

}
}

Saleh

[Attaullah Shah]

It would be simple for us to answer if you paste an example of your data set. One potential issue might be with this line

 foreach x of varlist no_`var'{

change this the following. i.e.

foreach x of varlist no_*{ 
 recode `x' (.=0) if fp_offered=1

Again, without seeing the data, it is just an educated guess.

[Nick Cox]

For once the data seem irrelevant to the syntax.

This can be slimmed down. First, correct the test = 1 to == 1 as otherwise the code will fail.

Now note that the inner loop is a loop over one variable, namely reducible to a single statement.

Each new variable will be 1 if

`var' > 1 & `var' < . 

and otherwise 0 if

fp_offered == 1

and otherwise missing.

That all can be rewritten

foreach var of varlist stock_* {    
    gen no_`var' = cond(`var' > 1 & `var' < ., 1, cond(fp_offered == 1, 0, .))  
}

I am guessing here that the wildcard stock_* expands to the variables listed; if that is not true then Saleh does indeed need to use the list of variable names he spelled out.

Now whether you use cond() is a matter of programming taste. Some people find nested conditions hard to read but the trick is to think through them in words in some fashion like the sentence I have put in bold above. (If bold does not show up in your mailer, it is the sentence starting Each variable ....)

For a tutorial on cond() see http://www.stata-journal.com/sjpdf.html?articlenum=pr0016 and for an example in which three nested cond() calls are natural see http://www.stata.com/support/faqs/data-management/leap-year-indicators/

As in elementary algebra the parentheses ( ) must match.

If despite this advocacy you still find two statements clearer, go for it:

foreach var of varlist stock_* {
      gen no_`var' = 1 if `var' > 1 & `var' < .
      replace no_`var' = 0 if `no_var' == . & fp_offered == 1
}

Avoiding recode whenever possible as I tend to do is also arbitrary taste. Those who have spent a lot of time around some other statistical packages tend to regard it as a favourite friend.

But -- to return to the title of the thread -- there is no need for two loops at all.

[Saleh Babazadeh]

I appreciate your input Nick.
Thanks Attaullah.

[Kasim Ortiz]

Nick, I've posted a similar inquiry except mine issue involves three loops in one and a outreg2 issue. Is it possible that you could please look at my post and provide feedback????

[Nick Cox]

Kasim: I would look at it if I knew where it was posted. If you're implying a personal email then please know in advance that I typically decline to answer Stata-related questions sent to me privately by people I don't know unless they concern bugs or limitations of my own programs.

As an extension of http://www.statalist.org/forums/help#adviceextras #2 it's important to underline that private queries answered privately are of limited or no benefit to anybody else whereas the whole point of a forum is that others can find threads interesting or useful. Equally crucial, any question can benefit from the ideas of several and a thread here is less subject to the vagaries of who is asleep, busy, enjoying a hard-earned break or otherwise unavailable.

There is also the small limitation that my time is finite. I suspect that other highly active people would have similar personal policies.

Crucial detail: I never use outreg2 (SSC) and have no interest or expertise in answering questions about it. Note that the author is not a member here.

[Nick Cox]

I see that Kasim was alluding to http://www.statalist.org/forums/foru...oping-sequence