Hi, Try this: set.seed(248) lst1<- lapply(1:1000,function(i) matrix( sample(0:1,15*100,replace=TRUE),ncol=100,dimnames=list(paste("Island",LETTERS[1:15]), paste0("D",sprintf("%04d",1:100))))) lst2<-lst1[sapply(lst1,function(x) any(colSums(x)==0))] ##The above steps are just to create some matrices with zeros in all the "islands" mat1<-lst2[[1]] mat1[,colSums(mat1)==0,drop=FALSE] # D0038 #Island A 0 #Island B 0 #Island C 0 #Island D 0 #Island E 0 #Island F 0 #Island G 0 #Island H 0 #Island I 0 #Island J 0 #Island K 0 #Island L 0 #Island M 0 #Island N 0 #Island O 0 colnames(mat1)[colSums(mat1)==0] #[1] "D0038" mat2<-lst2[[3]] colnames(mat2)[colSums(mat2)==0] #[1] "D0086"
A.K. ----- Original Message ----- From: Elaine Kuo <elaine.kuo...@gmail.com> To: "r-help@r-project.org" <r-help@r-project.org> Cc: Sent: Friday, September 20, 2013 7:14 PM Subject: [R] search species with all absence in a presence-absence matrix Dear list I have a matrix composed of islandID as rows and speciesID as columns. IslandID: Island A, B, C….O (15 islands in total) SpeciesID: D0001, D0002, D0003….D0100 (100 species in total) The cell of the matrix describes presence (1) or absence (0) of the species in an island. Now I would like to search the species with absence (0) in all the islands (Island A to Island O.) Please kindly advise the R code for the search purpose. Thank you. Elaine [[alternative HTML version deleted]] ______________________________________________ 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.