[R] Equivalent to Stata egen

[Stas Kolenikov]

See, we just jave different expectations of what is to be seen in the
help system, and are used to different formats. Yes, Stata thinks of
data as a rectangular array (although it stores it in memory, unlike
SAS). The inputs to -egen-, as well as the values produced, depend on
the particular function -fcn- and are described in subsections on
those individual functions. That is mentioned at the top of the page.
There is a pretty much standard syntax of most Stata commands (command
name followed by variables it is applied to or expression to be
computed followed by if conditions on observations followed by comma
options ), and -egen- more or less satisfies that syntax. A Stata user
equipped with the basic concepts of the assignment command -generate-
(which -egen- is said to extend) and variable lists (-varlist- here
and there in the help file) would be able to make sense of this all.

I would rather translate R's ave() to Stata's -by- expression. Not all
of the -egen- functionality can be implemented via ave().

Looks like terseness is a prerequisite to doing anything in R though.
If I am telling you I am a newbie, the book abbreviations although
standard to everybody on this list may not mean much to me. I could
figure out "Regression Modeling Strategies" (although I was not
thinking about it as a book on R -- I probably did not read it far
enough :) ), and V&R is Venables & Ripley. Right?

On 4/16/09, David Winsemius <dwinsemius at comcast.net> wrote:
> Terse is OK by me as long as I get told what goes in (allowable data types,
> argument names and effects) and what comes out. What seemed to be lacking in
> that Stata doc for egen was a description of the purpose or behavior and
> then could find no description of the values produced. Perhaps it is because
> Stata has an approach that everything is a rectangular array? Is everything
> assumed to create a new column of data as in SAS?
>
>  At any rate it looked to this casual non-user, reading that document, that
> egen creates a new variable aligned with its argument variables by applying
> various functions within groupings. That is pretty much what ave does. "ave"
> is not restricted to mean as a functional argument. As I said it was a
> guess.
>
>  The texts I used to get up to speed in R are several downloaded from the
> Contributed documents (including anything written by Venables), V&R MASS v
> 2, Harrell's RMS, Sarkar's Lattice, Chambers&Hastie SMiS and reading a lot
> of Q&A on this list.
>
>  --
>  David Winsemius
>
>  On Apr 16, 2009, at 11:57 AM, Stas Kolenikov wrote:
>
>
> > http://www.stata.com/help.cgi?egen -- it creates new
> variables dealing
> > with some special relatively non-standard tasks that don't boil down
> > to a one-line arithmetic expressions. For that reason, there will be
> > no equivalent to -egen- in general, as it has so many functions that
> > are so different. -rowtotal- is of course just a shorthand for sum(),
> > except for treatment of missing values ( ifelse(is.na(x),0,x ). But
> > -anycount- is a moderately complicated double cycle over variables and
> > list of values (40 lines of underlying Stata code, including parsing
> > and labeling the resulting variables)... which will probably become a
> > triple R cycle including the cycle over observations, although the
> > latter can probably be avoided.
> >
> > Yes, R documentation looks exteremely terse to me as a regular Stata
> > user. I am used to seeing the concpets explained well, even in the
> > help files, and certainly more so in the shelved books. As every
> > option and every part of the syntax is devoted at least three to five
> > sentences, and the most common uses are exemplified, I can usually
> > figure out how to run a particular task relatively quickly. (The data
> > management tricks, which is what Peter was asking about above, are
> > probably an exception: you either know them, or you don't. In this
> > example, I don't know the corresponding R tricks, although I can
> > probably brute force the solution if I needed to.) The fraction of
> > commands in R that I personally have been coming across that are
> > comparably well documented is about a quarter. For other, it is either
> > a guesswork+CRANning+googling around or "Forget it, I'll just go back
> > to Stata to do it" after a few futile attempts. May be I just don't
> > know where to look for the good stuff, but it is certainly outside R
> > as a package+its documentation.
> >

-- 
Stas Kolenikov, also found at http://stas.kolenikov.name
Small print: I use this email account for mailing lists only.