[R] extract columns from a dataframe
Prof Brian Ripley
ripley at stats.ox.ac.uk
Mon Jul 5 16:23:54 CEST 2004
On 5 Jul 2004, Yves Magliulo wrote:
> see colnames()
> simple use, good result.
Not really correct use, though. A data frame has names for its columns,
and a matrix has colnames.
> ex: if df is your data.frame and toto = the column name you want to
> extract do:
> df2<-df[,colnames(df)==toto)] #extract all toto column
df["toto"] is much easier (and you do need the quotes, I believe). It
even works with a vector of names.
> Le lun 05/07/2004 à 14:53, Rado Bonk a écrit :
> > Dear R users,
> > I'm coming back to R after while. I have a data frame with 200 columns,
> > each column has a name. How to extract all columns to a new dataset, but
> > the specified (by names) ones?
I read that as meaning `all except the specified columns'.
> > I was playing with that for a little bit using the vector syntax but got
> > several syntax errors.
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 272866 (PA)
Oxford OX1 3TG, UK Fax: +44 1865 272595
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