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st: Re: How do you drop the variable -(e)- from the data?

From   Roger Newson <>
Subject   st: Re: How do you drop the variable -(e)- from the data?
Date   Thu, 06 Nov 2003 13:34:48 +0000

At 11:58 06/11/03 +0000, Nick Cox wrote:
xcontract foreign rep78, list(, sepby(foreign))

is evidently legal. Does that solve part of the problem?


Yes. In fact, it solves all the problem. So the problem was simply the expansion of the unexpanded "*" varlist. I should therefore add square brackets to the varlist in the -list()- option of the syntax of -xcontract-, -xcollapse-, -parmby- and -parmest-, because

list(varlist [if exp] [in range] [, list_options ] )

should really be

list( [varlist] [if exp] [in range] [, list_options ] )

Thanks for solving my problem. (And thanks in advance to StataCorp for fixing the feature and reducing possible confusion amongst naive users who might use "*" just the same.)


Roger Newson
> The reason I wanted to drop "(e)" was that it was causing
> confusing output
> to come from my -xcollapse- and -xcontract- packages,
> downloadable from SSC
> or from my website. These are extended versions of -collapse- and
> -contract-, respectively, and create output data sets that
> can be listed
> and/or saved to disk and/or saved to memory (overwriting
> any existing
> data). If the user types, in Stata 8,
> sysuse auto, clear
> regress mpg weight
> xcontract foreign rep78, list(*, sepby(foreign))
> then -xcontract- lists the frequencies of each combination
> of -foreign- and
> -rep78-, both as numbers and as a percentage of all cars,
> and also lists
> the variable "(e)", which could be confusing for naive
> users. It is helpful
> to know that this will be fixed, and that, in the meantime,
> "(e)" will not
> be saved to the output data set produced by the -saving()-
> option of
> -xcontract- or -xcollapse-.

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Roger Newson
Lecturer in Medical Statistics
Department of Public Health Sciences
King's College London
5th Floor, Capital House
42 Weston Street
London SE1 3QD
United Kingdom

Tel: 020 7848 6648 International +44 20 7848 6648
Fax: 020 7848 6620 International +44 20 7848 6620
  or 020 7848 6605 International +44 20 7848 6605

Opinions expressed are those of the author, not the institution.

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