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Re: st: macro of macros?


From   Nick Cox <njcoxstata@gmail.com>
To   statalist@hsphsun2.harvard.edu
Subject   Re: st: macro of macros?
Date   Mon, 7 Nov 2011 16:46:46 +0000

I don't think so. I just was emphasising, pedantically if anyone wants
to say so, that  "Fundamentally, Stata does not make it easy to use
data structures other than the dataset and macros" was not quite
correct. But the other stuff does not I think help here in any
important way.

Macro processing in Stata is an odd thing to get used to, unless you
have a prior history of Unix shell programming, and who does? However,
some people learn programming from Stata programming and then Mata
looks very odd. (Where are the macros?).

Nick

On Mon, Nov 7, 2011 at 3:46 PM, Billy Schwartz <wkschwartz@gmail.com> wrote:
> Nick,
>
> Fair points. Is there a way to do what Ana was looking to do using
> matrices, treating them as arrays of arrays perhaps?
>
>
> On Mon, Nov 7, 2011 at 10:02 AM, Nick Cox <njcoxstata@gmail.com> wrote:
>>
>> Billy has good advice which repeats some already given in this thread,
>> but his initial statement deserves a challenge.
>>
>> 1. Stata has fair support for matrices and very good support for
>> matrices through Mata. Those are _major_ exceptions to the
>> generalisation in the first sentence.
>>
>> 2. Billy is right that attacking this problem through OOP would be
>> clunky in Stata. But it would be clunky in almost any language and
>> crazy in most to set up code for sets of macros in such terms.
>>
>> On Mon, Nov 7, 2011 at 2:52 PM, Billy Schwartz <wkschwartz@gmail.com> wrote:
>> > Ana,
>> >
>> > Fundamentally, Stata does not make it easy to use data structures
>> > other than the dataset and macros. Technically, it supports OOP, which
>> > you would use in most other languages to solve this kind of problem,
>> > but the syntax is so clunky, you would never write a Stata class
>> > unless there's no other way. Here's my suggestion for solving this
>> > problem using macros.
>> >
>> > Each 'set#' macro you create is like an array, and you want an array
>> > of these arrays, which you'll call 'sets'. You'll use the # at the end
>> > of each macro name 'set#' as the index within 'sets'. Name these
>> > macros set1 ... setN  WITH NO SKIPS, so if you need to remove set 4,
>> > you'll take the contents of setN and put it in set4 and delete setN.
>> > You'll use "double indirection", a macro with in a macro, to
>> > substitute in the # in the loops. `set1' becomes pointer = 1;
>> > `set`pointer''. Notice the nested macro expansion operators.
>> >
>> > local set1 x1 x2
>> > local set2 x2 x3
>> > local set3 x1 x3
>> >
>> > //the following block is like your local sets ""`set'*""
>> > local pointer = 1
>> > while ("`set`pointer++''" != "") { /*help macro (the ++ AFTERthe
>> > pointer macro name increments the pointer macro AFTER the macro is
>> > expanded)*/
>> > local sets `sets'  set`pointer'
>> > }
>> > local --pointer //decrements the pointer to point to the last position
>> > in the sets array. only really necessary if you use version 2 below
>> >
>> > //version 1
>> > foreach xvars of local sets {
>> > regress y ``xvars'' //notice the double indirection used here
>> > }
>> >
>> > //version 2. not necessarily better or worse than version 1
>> > forvalues i = 1/`pointer' {
>> > regress y `set`i'' //notice double indirection here
>> > }
>> >
>> > On Sun, Nov 6, 2011 at 10:01 AM, Maria Ana Vitorino
>> > <vitorino@wharton.upenn.edu> wrote:
>> >>
>> >> Dear statalist users,
>> >> I've only recently started experimenting with macros and I have the following question: can we have a macro of macros and loop through the different sub-macros without having to set beforehand  how many sub-macros there are in the macro? Maybe it's easier to understand what I'm looking for with an example:
>> >>
>> >> I know that the following can be done:
>> >>
>> >> local set1 "x1 x2"
>> >> local set2 "x2 x3"
>> >> local sets ""`set1'" "`set2'""  ***
>> >>
>> >> foreach xvars of local sets {
>> >> reg y xvars
>> >> }
>> >>
>> >> But, instead of having to list all the macros in the line ***, can we have something like:
>> >>
>> >> local set1 "x1 x2"
>> >> local set2 "x2 x3"
>> >>
>> >> local sets ""`set'*""
>> >>
>> >> foreach xvars of local sets {
>> >> reg y xvars
>> >> }
>> >>
>> >>
>> >> Ideally I would like to add (or remove) sets as a please so I wouldn't like to have to keep updating the line *** everytime I do so...

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