Thank you for your reply, but I am still confused. Let me clarify... ...my problem isn't with zoo-ness per se. With zoo objects, there appears to be zoo-matrices and zoo-vectors.
My problem is this - I start with a zoo-matrix: > x <- m[1,,drop=FALSE] > x inp 2003-02-01 5 > is.matrix( x ) [1] TRUE ------------------------------------ and another zoo-matrix: > y <- lag(m,-1) > y inp 2003-02-02 5 2003-02-03 9 2003-02-04 4 2003-02-05 2 > is.matrix( y ) [1] TRUE ------------------------------------ and somehow, when I rbind() them together, I get a zoo-vector: > z <- rbind( x, y ) > z 2003-02-01 2003-02-02 2003-02-03 2003-02-04 2003-02-05 5 5 9 4 2 > is.matrix( z ) [1] FALSE > is.zoo( z ) [1] TRUE ------------------------------------ Yes, I realize that x, y, and z are still zoo's (as they should be). But the part I can't resolve is, z has turned into a zoo-vector. Unfortunately, none of the 3 solutions you gave are zoo-matrices: > is.matrix( as.zoo(rbind(m[1,,drop=FALSE], lag(m,-1) )) ) [1] FALSE > is.matrix( c(m[1,,drop=FALSE], lag(m,-1) ) ) [1] FALSE > is.matrix( merge(c(m[1,,drop=FALSE], lag(m,-1) )) ) [1] FALSE ------------------------------------ I was using dim() as a indirect test for matrices where I could be using is.matrix() to be more explicit; before this, I did not know if is.matrix() would work on a zoo-matrix. Now, I know! It seems to me that I need to write a specialized version of my function for vectors (whether a plain vector or a zoo vector) and another version for matrices (whether a plain matrix or a zoo matrix). Luckily, I am only dealing with 2d matrices. But I don't know if I can avoid using really ugly class-based code testing for is.zoo(m) and is.matrix(m), etc... ...but even worse, my code works for a multi-column 2d zoo matrices, but not for a single-column 2d zoo matrix. Gabor Grothendieck mentioned in another thread that if I use S3 generics on zoo, I can avoid using a switch on zoo and non-zoo types. But unfortunately, his example, like mine, only works on a multi-column zoo-matrix, but fails on a single-column zoo-matrix (gets converted to a zoo-vector). So I don't have a solution yet. I am still trying to write something which will take a: 1. vector and return a vector 2. single-column matrix and return a single-column matrix 3. multi-column matrix and return a multi-column matrix 4.-6. zoo versions of 1.-3. I think solutions for 1, 3, 4, and 6 have been posted, but it is not clear to me how I should handle 2 and the zoo-version of 2 yet. -- View this message in context: http://www.nabble.com/Problem-with-zoo-and-rbind%28%29-converting-matrix-to-vector-tp22638959p22641961.html Sent from the R help mailing list archive at Nabble.com. ______________________________________________ R-help@r-project.org mailing list https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide http://www.R-project.org/posting-guide.html and provide commented, minimal, self-contained, reproducible code.