Message-ID: <Pine.LNX.4.64.0602131912400.17719@gannet.stats.ox.ac.uk>
Date: 2006-02-13T19:18:31Z
From: Brian Ripley
Subject: indexing via a character matrix?
In-Reply-To: <43F0CFEF.3070900@inf.ed.ac.uk>
On Mon, 13 Feb 2006, Roger Levy wrote:
> Hi,
>
> Is it possible to index via a character matrix? For example, I would
> like to do the following:
>
> cont.table <- table(df1$A,df1$B) # df1 a data frame with factors A and B
> cont.table[cbind(df2$A,df2$B)] # df2 a smaller data frame with some
> # pairings of values for A and B
>
> but the second step does not work -- I guess that matrices to be used
> for indexing this way must be numeric. Is there a way to index multiple
Numeric or logical.
> character tuples out of a contingency table without resorting to writing
> loops?
What are you trying to do here? One possibility is that you meant
comt.table[df2$A, df2$B]
and another is
ind1 <- match(df2$A, df1$A)
ind2 <- match(df2$B, df1$B)
cont.table[cbind(ind1, ind2)]
and I am not certain which.
--
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