indexing via a character matrix?
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