Hi, Try this: a1<-a a1[rowSums(is.na(a1))==1][ is.na(a1[rowSums(is.na(a1))==1])]<-0 library(matrixStats) c1<- cbind(a,rowDiffs(a1)) c1 # [,1] [,2] [,3] #[1,] 2 5 3 #[2,] 3 8 5 #[3,] 4 NA -4 #[4,] NA 8 8 #[5,] NA NA NA
identical(c,c1) #[1] TRUE A.K. ----- Original Message ----- From: Pedro Mardones <mardone...@gmail.com> To: R-help@r-project.org Cc: Sent: Wednesday, March 13, 2013 5:43 PM Subject: [R] calculating column difference in a matrix Dear R users; Consider the following toy example: a <- matrix(c(2,3,4,NA,NA,5,8,NA,8,NA), 5, 2) b <- cbind(a,apply(a, 1, diff, na.rm = TRUE)) What I would like be able to get is: c <- matrix(c(2,3,4,NA,NA,5,8,NA,8,NA,3,5,-4,8,NA), 5, 3) i.e., for each row if both values (column 1 and 2) are NA then the difference must return NA, but if any of those two values is different from NA (!is.na), I would like to actually perform the difference (something like assigning 0 instead to NA to the cell). I'd appreciate any hint or comment Best, Pedro BTW: the reason of this is that I'm trying to build an error checking procedure for a big dataset I have ______________________________________________ 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. ______________________________________________ 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.
