On May 19, 2013, at 16:22 , Jinsong Zhao wrote: > Hi there, > > I have the following code: > > z <- matrix(c("A", "A", "B", "B", "C", "C", "A", "B", "C"), ncol = 3) > apply(z, 2, table, c("A", "B", "C")) > > which give correct results. > > However, the following code: > > apply(z[,1,drop=FALSE], 2, table, c("A", "B", "C")) > > which does not give what I expect. I have been thought it should give the > same result as: > > apply(z, 2, table, c("A", "B", "C"))[[1]] > > What's the difference? Does apply not apply to column vector?
To clue the casual reader in, the former gives: > apply(z, 2, table, c("A", "B", "C")) [[1]] A B C A 1 1 0 B 0 0 1 [[2]] A B C B 1 0 0 C 0 1 1 [[3]] A B C A 1 0 0 B 0 1 0 C 0 0 1 whereas the latter gives the first of the tables strung out as a 6x1 matrix. This is a generic awkwardness of apply(). It tries to simplify the result (similar to sapply), so if the result for all columns have the same length (say, k), it converts them to a (k x C) matrix. If the results are incommensurable, it gives up and returns a list. So if we modify the code to always give a 3x3 matrix, the following happens: > ABC <- LETTERS[1:3] > apply(z, 2, function(x) table(factor(x, levels=ABC), ABC)) [,1] [,2] [,3] [1,] 1 0 1 [2,] 0 1 0 [3,] 0 0 0 [4,] 1 0 0 [5,] 0 0 1 [6,] 0 1 0 [7,] 0 0 0 [8,] 1 0 0 [9,] 0 1 1 (This, incidentally, also answers your question below.) You can't turn simplification off in apply(), but a passable workaround is > tapply(z, col(z), function(x) table(factor(x, levels=ABC), ABC)) $`1` ABC A B C A 1 1 0 B 0 0 1 C 0 0 0 $`2` ABC A B C A 0 0 0 B 1 0 0 C 0 1 1 $`3` ABC A B C A 1 0 0 B 0 1 0 C 0 0 1 > > Another question: how to output the table in squared matrix (or data frame)? > For example: > > > table(c("C", "B", "B"), c("A", "B", "C")) > > A B C > B 0 1 1 > C 1 0 0 > > I hope to get the result something like: > > A B C > A 0 0 0 > B 0 1 1 > C 1 0 0 > > Is there a way that can output that? > > Any suggestions will be really appreciated. Thanks in advance. -- Peter Dalgaard, Professor, Center for Statistics, Copenhagen Business School Solbjerg Plads 3, 2000 Frederiksberg, Denmark Phone: (+45)38153501 Email: pd....@cbs.dk Priv: pda...@gmail.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.