[R] Selecting cases from a data frame

[Prof Brian D Ripley]

On Tue, 19 Mar 2002, Andrew Perrin wrote:

> My apologies if this is obvious - I assume it is but still can't seem to
> make it work.
>
> I've got a data frame acps.df; I want to run an analysis on a subset of
> that data frame, defined as the subset for which the value of OGMCAT (a
> column in the data frame) is anything OTHER than 9, 11, or 12.  So I'd
> like to define a new data frame that consists of the same variables as in
> acps.df, but without those cases. I tried this:
>
> > acps.nopg.df<-acps.df[(acps.df$OGMCAT != 9) & (acps.df$OGMCAT != 11) &
> (acps.df$OGMCAT !=  12)]
>
> but got this:
>
> Error in "[.data.frame"(acps.df, (acps.df$OGMCAT != 9) & (acps.df$OGMCAT
> !=  :
>         undefined columns selected

acps.nopg.df<-acps.df[!(acps.df$OGMCAT) %in% c(9,10,12)), ]
                                                        ^
You omitted a critical comma: 1D indexing of data frames is by columns.
Using match (via %in% or is.element) is more elegant and clearer.

-- 
Brian D. Ripley,                  ripley at stats.ox.ac.uk
Professor of Applied Statistics,  http://www.stats.ox.ac.uk/~ripley/
University of Oxford,             Tel:  +44 1865 272861 (self)
1 South Parks Road,                     +44 1865 272860 (secr)
Oxford OX1 3TG, UK                Fax:  +44 1865 272595

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