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# RE: st: What is EGEN_Varname and EGEN_SVarname ?

 From Pradipto Banerjee To "statalist@hsphsun2.harvard.edu" Subject RE: st: What is EGEN_Varname and EGEN_SVarname ? Date Tue, 31 Jul 2012 07:47:36 -0500

```Nick, That's very interesting. I wasn't aware that this kind of usage of ":" is possible. It's another undocumented feature.

-----Original Message-----
From: owner-statalist@hsphsun2.harvard.edu [mailto:owner-statalist@hsphsun2.harvard.edu] On Behalf Of Nick Winter
Sent: Tuesday, July 31, 2012 8:41 AM
To: statalist@hsphsun2.harvard.edu
Subject: Re: st: What is EGEN_Varname and EGEN_SVarname ?

Not that this is the advice you are looking for, but I tend to solve
this sort of problem like this:

local newvars test1 test2
local oldvars price mpg

forval i=1/`: word count `newvars'' {
egen `: word `i' of `newvars'' = sum(`: word `i' of oldvars'')
}

or

local newvars test1 test2
local ptiles 10 90

forval i=1/`: word count `newvars'' {
egen `: word `i' of `newvars'' = pctile(price), p(`: word `i' of
ptiles'')
}

s

On 7/30/2012 6:50 PM, Pradipto Banerjee wrote:
> In case, it helps why I was asking about EGEN_Varname and EGEN_SVarname, this is a command of the-egenmult- code I have written that repeatedly calls -egen-. The way it works is as follows:
>
> . sysuse auto, clear
>
> Example # 1
> . by foreign, sort: egenmult {test1 test2} = sum({price mpg})
>
> It works equivalently as:
>
> . sort foreign
> . by foreign: egen test1 = sum(price)
> . by foreign: egen test2 = sum(mpg)
>
> Example # 2
> . drop test1 test2
> . by foreign, sort: egenmult float {test1 test2} = pctile(price), p({10 90})
>
> It works equivalent as:
>
> . sort foreign
> . by foreign: egen float test1 = pctile(price),p(10)
> . by foreign: egen float test2 = pctile(price),p(90)
>
> I've been trying to see if I'm missing anything in the code below. Thanks.
>
> -----
> program define egenmult, byable(onecall) sortpreserve
>          local fullexp `0'
>          gettoken type 0 : 0, parse(" ")
>          local restexp `"`0'"'
>
>          /* gen a list of all possible types */
>          local types "byte int long float double"
>          forvalues i=1(1)244 {
>                  local types "`types' str`i'"
>          }
>          local typegiven strpos(`"`types'"',`"`type'"')
>          if `typegiven' > 0 local fullexp `restexp'
>          else local type
>
>          /* get the number & locations of the { } */
>          local partexp = `"`fullexp'"'
>          local curvefnd = 0
>          local numbrak = 0
>          local allopenpos
>          local allclosepos
>          local alloptions
>          while `curvefnd' == 0 {
>                  local openpos = strpos(`"`partexp'"',"{")
>                  if `openpos'>0 {
>                          local allopenpos `allopenpos' `openpos'
>                          local closepos = strpos(`"`partexp'"',"}")
>                          if `closepos' == 0 error 198
>                          local allclosepos `allclosepos' `closepos'
>                          local numbrak = `numbrak'+1
>                          if `"`alloptions'"'=="" {
>                                  local newoptions = substr(`"`partexp'"',`openpos'+1,`closepos'-`openpos'-1)
>                                  local alloptions `"`newoptions'"'
>                                  local numloop = wordcount(`"`newoptions'"')
>                          }
>                          else {
>                                  local newoptions = substr(`"`partexp'"',`openpos'+1,`closepos'-`openpos'-1)
>                                  if `numloop'!=wordcount(`"`newoptions'"') error 198
>                                  local alloptions `"`alloptions'"' `"`newoptions'"'
>                          }
>                  }
>                  else {
>                          local curvefnd = 1
>                  }
>                  local partexp = subinstr(`"`partexp'"',"{","!",1)
>                  local partexp = subinstr(`"`partexp'"',"}","!",1)
>          }
>          local tollen = strlen(`"`partexp'"')
>
>          /* recreate & run the individual commands */
>          forvalues iloop=1(1)`numloop' {
>                  forvalues jbrak=1(1)`numbrak' {
>                          if `jbrak'==1 {
>                                  local jthbrakopen : word `jbrak' of `allopenpos'
>                                  local newexp = substr(`"`partexp'"',1,`jthbrakopen'-1)
>                                  local repexp : word `jbrak' of `"`alloptions'"'
>                                  local repexp = word(`"`repexp'"',`iloop')
>                                  local newexp = `"`newexp'"' + " " + `"`repexp'"' + " "
>                          }
>                          else {
>                                  local jthbrakopen : word `jbrak' of `allopenpos'
>                                  local jprevbrak = `jbrak'-1
>                                  local jprevbrakclose : word `jprevbrak' of `allclosepos'
>                                  local newexp = `"`newexp'"' + " " + substr(`"`partexp'"',`jprevbrakclose'+1,`jthbrakopen'-`jprevbrakclose'-1)
>                                  local repexp : word `jbrak' of `"`alloptions'"'
>                                  local repexp = word(`"`repexp'"',`iloop')
>                                  local newexp = `"`newexp'"' + " " + `"`repexp'"' + " "
>                          }
>                  }
>                  local jprevbrakclose : word `numbrak' of `allclosepos'
>                  local newexp = `"`newexp'"' + substr(`"`partexp'"',`jprevbrakclose'+1,`tollen'-`jprevbrakclose')
>                  if _by() by `_byvars': egen `type' `newexp'
>                  else egen `type' `newexp'
>          }
>
> end
>
> -----
>
> -----Original Message-----
> From: owner-statalist@hsphsun2.harvard.edu [mailto:owner-statalist@hsphsun2.harvard.edu] On Behalf Of Pradipto Banerjee
> Sent: Monday, July 30, 2012 5:25 PM
> To: statalist@hsphsun2.harvard.edu
> Subject: RE: st: What is EGEN_Varname and EGEN_SVarname ?
>
> Thanks, Billy. After reading your email, I realized that perhaps my questions weren't clear. So, I thought to rewrite them:
>
> 1. One of the things I specifically asked was where did the -egen- code figure out that it was supplied with -by- or -bysort-.
>
> 2. On a standalone basis, what does it mean if we use "_all" such as in `"`args'"' =="_all"? I already AWARE of the usage(s) of _all in -drop _all-, -program drop _all- etc. This usage of `"`args'"' =="_all" is NOT documented in the programming manual!
>
> 3. In the -egen- code, what the following line achieve? Or intends to achieve?
>
> local args : subinstr local args "`_sortindex'"  "", all word
>
> 4. Regarding your comment "The global macros need to be defined so they can be passed to the other functions (which is why Nick explicitly mentioned that they are there because local macros would not work in this context).", I was specifically asking: why do they need to be passed on to other functions and why do they need to be defined twice?
>
> 5. Yes, I have read the Programming Manual - and none of the questions I have asked can be resolved using the Manual. Kit Baum's book as the name suggests is an Introduction. Please let me know if that book the specifically any of the questions I asked.

>
> Best.
>
>
> -----Original Message-----
> From: owner-statalist@hsphsun2.harvard.edu [mailto:owner-statalist@hsphsun2.harvard.edu] On Behalf Of William Buchanan
> Sent: Monday, July 30, 2012 5:10 PM
> To: statalist@hsphsun2.harvard.edu
> Subject: RE: st: What is EGEN_Varname and EGEN_SVarname ?
>
>
> I'll try to answer what I can, but it may not be much and others on the list
> would likely have much more refined/precise answers.
>
> 1. The lines of code:
>
>    if _by() {
>                  local byopt "by(`_byvars')"
>                  local cma ","
>          }
>
> might be what you are looking for, but you should also read the help file
> for the -byable- option in the programming manual.  This will better explain
> things.
>
> 2. Not sure about all of your question here, but you should consider the
> context in which this line occurs
>
> if `"`args'"' == "_all" | `"`args'"' == "*" {
>                  version 7.0, missing
>                  unab args : _all
>                  local args : subinstr local args "`_sortindex'"  "", all
> word
>                  version 6.0, missing
>          }
>
> Which seems like it is parsing different ways that you could include the
> entire varlist in your dataset.  And _all is used in more than just -drop-.

> For example, -log query _all- or -program drop _all- are other uses of
> "_all".
>
> 3. The global macros need to be defined so they can be passed to the other
> functions (which is why Nick explicitly mentioned that they are there
> because local macros would not work in this context).
>
>
> Have you read the programming manual for Stata yet?  If not I would highly
> suggest going through that and possibly looking into other resources (Kit
> Baum's book is pretty awesome).  Otherwise, you could probably just as
> easily create a work around using tempvars that you could combine into a
> single variable that is stored at the end of the routine with a loop.
>
> HTH,
> Billy
>
>
>
>
> -----Original Message-----
> From: owner-statalist@hsphsun2.harvard.edu
> [mailto:owner-statalist@hsphsun2.harvard.edu] On Behalf Of Pradipto Banerjee
> Sent: Monday, July 30, 2012 1:47 PM
> To: statalist@hsphsun2.harvard.edu
> Subject: RE: st: What is EGEN_Varname and EGEN_SVarname ?
>
> Billy,
>
> I'm primarily trying to understand Stata syntax within the -egen- code to
> write my "own" function rather than modify the -egen- code. Perhaps you can
> help me. For instance,
>
>
> 1. How does the egen function handle the "by" part:
>
> . by var1: egen ...
> . bysort var1 (var2): egen ...
>
> i.e., where in the egen code, does it figure out that it needs to sort
> before doing a by operation etc (i.e. where does it figure out that it was
> supplied with -by- instead of -bysort- etc). Similarly, in another part of
> the function, it's written
>
> . capture noisily _g`fcn' `type' `dummy' = (`args') `if' `in' /*
>                  */ `cma' `byopt' `options'
>
> Why is the "by" part done this way?, i.e. why isn't this given as
>
> . capture noisily by _byvars: _g`fcn' `type' `dummy' = (`args') `if' `in' ,
> `options'
>
>
> 2. In the part of the code where it is written:
>
> (a) . local args : subinstr local args "`_sortindex'"  "", all word
>
> Why are we changing all instances of _sortindex as blanks? Isn't the
> sortindex typically like __000000 (or something similar), and it isn't
> normally provided when a person is calling the egen function?
>
> (b) . if `"`args'"' =="_all"
>
> Usually, I had seen _all been used as drop _all. What does the above part of
> the code mean?
>
> 3. (a) Why do we need to define EGEN_SVarname and EGEN_Varname to `name' and
> _sortindex before calling the _g`fcn', AND (b) why do we need to define them
> again to Null?
>
> Thanks
>
>
>
>
>
>
> -----Original Message-----
> From: owner-statalist@hsphsun2.harvard.edu
> [mailto:owner-statalist@hsphsun2.harvard.edu] On Behalf Of William Buchanan
> Sent: Monday, July 30, 2012 1:00 PM
> To: statalist@hsphsun2.harvard.edu
> Subject: RE: st: What is EGEN_Varname and EGEN_SVarname ?
>
>
> Another important thing to consider, with regards to Nick's advice, is that
> he is basically trying to prevent you from making any changes to your
> installed copy of Stata that might "break" it.  If you're changing the
> global macros in the egen files then you run the risk of making a change
> that prevents egen from working correctly in the future.  If you wanted to
> see what those variables are, you could do something like:
>
> viewsource egen.ado (copy the material in the window into the do file editor
> or another text editor of your choice)
>
> where this is you can use the -sysdir- command)
>
> pick the function that you were trying to modify and do the same thing
> (e.g., copy the source into a new file myconcat.ado for example).
>
> Now if you make a call to -myegen- make sure that you are using the function
> that you've duplicated and you can change the global macros in your
> duplicate files.
>
> The point, however, is to avoid editing any of the files that are native to
> the Stata installation unless you're willing to risk making potentially
> harmful changes.  Additionally, Nick also provided you with an example
> earlier illustrating how you could make the egen subroutine that you were
> interested in byable, so you could just start working with that code and
> modifying it as necessary.
>
> HTH,
> Billy
>
>
>
> -----Original Message-----
> From: owner-statalist@hsphsun2.harvard.edu
> [mailto:owner-statalist@hsphsun2.harvard.edu] On Behalf Of Nick Cox
> Sent: Monday, July 30, 2012 9:41 AM
> To: statalist@hsphsun2.harvard.edu
> Subject: Re: st: What is EGEN_Varname and EGEN_SVarname ?
>
> I am mixing explanations and advice on different levels. Feel free to take
> the explanations when correct and ignore the advice if it doesn't appeal.
> Otherwise I think Maarten's reply to you captures my attitude well. It is a
> defining characteristic of a discussion list that people aren't obliged to
> offer exactly the kind of support that posters of questions might prefer.
>
> Nick
>
> On Mon, Jul 30, 2012 at 8:48 AM, Pradipto Banerjee
>> Nick
>>
>> I don't understand your line of thought ... you actually want me NOT
>> to
> advance my understanding of programming in Stata? Why are some folks allowed
> to understand advanced programming and others not?
>> Sorry to say this, but one huge negative of Stata is that there is so
>> much
> undocumented stuff - and for efficient programming we have to repeatedly
> rely on email lists like this.
>>
>> -----Original Message-----
>> From: owner-statalist@hsphsun2.harvard.edu
>> [mailto:owner-statalist@hsphsun2.harvard.edu] On Behalf Of Nick Cox
>> Sent: Saturday, July 28, 2012 9:33 AM
>> To: statalist@hsphsun2.harvard.edu
>> Subject: Re: st: What is EGEN_Varname and EGEN_SVarname ?
>>
>> These are names of globals defined in -egen- to communicate between
>> programs, which manifestly can't be done through locals, apart from
>> using non-documented features. If you're following my earlier advice
>> you will leave them in peace.
>>
>> Nick
>>
>> On 27 Jul 2012, at 16:03, Pradipto Banerjee
>>   > wrote:
>>
>>> I noticed some of the codes, e.g. _ggroup2 use EGEN_Varname and
>>> EGEN_SVarname and recently one of the codes shared by Nick (called
>>> ereplace) use these. What is EGEN_Varname and EGEN_SVarname ?
>> *
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```