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Re: st: foreach and forvalues combined


From   "Fabian Schönenberger" <sch.f@gmx.ch>
To   statalist@hsphsun2.harvard.edu
Subject   Re: st: foreach and forvalues combined
Date   Wed, 04 Jul 2012 16:56:10 +0200

Many thanks for the quick replies. Let me shortly describe what I want:

First, I sorted all stocks according to their annually market cap in 5 size portfolios = sizep5. Now, I need to create subportfolios; for each sizep5 (1 to 5) I want to create 5 subportfolios according to the annually BM-ratios of each company in each year. The breakpoints are considered with the condition bm<bm4 (which will change to bm<bm8 & bm>bm4 etc.). 

So, I have 3 conditions to consider: company Y in which sizeportfolio, reveals what BM-ratio in which year. Three conditions are too much for me, so I decided to the breakpoint condition manually, but I would like to automate the others.  

So, I need a variable which indicates first, what sizep5 portfolio the company belongs to, and then what bmp5 portfolio it belongs to. I cannot combine these two variables (would be the simplest way!) because I have to consider these breakpoints. Is the approach clearer?

How does Stata know that forval i = 1/5 corresponds to the sizep5 variable?

I apply 1975/2012 in the looping formula because with  

generate sizebmp5=11 if bm<bm4 & sizep5==1 & timeyear==1975

I only build subportfolios for 1975, but if sizep5 is other than 1, Stata should also consider 1975. 

Many thanks for your support!




-------- Original-Nachricht --------
> Datum: Wed, 4 Jul 2012 15:19:37 +0100
> Von: Nick Cox <njcoxstata@gmail.com>
> An: statalist@hsphsun2.harvard.edu
> Betreff: Re: st: foreach and forvalues combined

> Regardless of whether you are right, the first problem Stata will see is
> that
> 
> foreach i of sizep5 1/5
> 
> is not a legal syntax for -foreach-. Look again at the help. It seems
> that what you want is just
> 
> foreach i of num 1/5
> 
> or (even simpler)
> 
> forval i = 1/5
> 
> Your inner loop seems unnecessary, as you would do the same thing
> regardless of which year it was. Also is 1975/2012 what you intend
> rather than 1976/2012?
> 
> More fundamentally, I doubt that even when you fix the Stata syntax
> you will get what you want. My hunch is that you want to classify
> firms according to what they were in 1975, and then spread the
> classification to other years, but if so you won't do it like this.
> Also, it seems odd that you keep no (apparent) track here of company
> identifiers.
> 
> However, I won't try to guess what you want, not least because I could
> be quite wrong. Nevertheless our problem is disentangling what you
> want from your mistakes in Stata syntax. So my advice is to set your
> syntax aside and show us a simple realistic example of what the data
> look like now and what you want to get.
> 
> On Wed, Jul 4, 2012 at 3:02 PM, "Fabian Schönenberger" <sch.f@gmx.ch>
> wrote:
> 
> > I am facing the following challenge with my panel data while trying the
> form different portfolios (double ranking with size and BM-ratio). After
> generating the variable sizebm5 with:
> >
> > generate sizebmp5=11 if bm<bm4 & sizep5==1 & timeyear==1975
> >
> > I want to loop the conditions sizep5== and timeyear==. Sizep5 is a
> variable consisting of numbers from 1 to 5 (1 small companies, 5 large
> companies). Timeyear is the time variable, 1975 to 2012. I am trying the following:
> >
> >
> > . foreach i of sizep5 1/5 {
> >   2. forvalues t = 1975/2012 {
> >   3. replace sizebmp5=1`i' if bm<bm4 & sizep5==`i' & timeyear==`t'
> >   4. }
> >   5. }
> >
> > However Stata says invalid syntax. I guess the problem is with
> sizebmp5=1`i' -> 1 stands for the first condition bm<bm4 (I will change this
> condition manually and then switch to 2 and so on). With `i' I want the variable
> signalling the corresponding sizep5 portfolio. Because this variable changes
> from 1 to 5, I need the term `i'; I also tried 1_`i' but it did not work.
> >
> 
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