Re: [R] indexing via a character matrix?

From: Roger Levy <rlevy_at_inf.ed.ac.uk>
Date: Tue 14 Feb 2006 - 09:51:26 EST

Prof Brian Ripley wrote:
> 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.
>

Hmm, I think neither one is what I wanted. After thinking more about it, I think what I would need is

ind1 <- match(df2$A,levels(df1$A))
ind2 <- match(df2$B,levels(df2$B))
cont.table[cbind(ind1,ind2)]

Does this make sense? Is there a more natural way to express this?

Many thanks,

Roger



R-help@stat.math.ethz.ch mailing list
https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide! http://www.R-project.org/posting-guide.html Received on Tue Feb 14 09:55:27 2006

This archive was generated by hypermail 2.1.8 : Fri 03 Mar 2006 - 03:42:29 EST