Hi David, Try: Check the output of: lapply(mm,function(x) x) #mm is matrix #and lapply(as.data.frame(mm),function(x) x)
sapply(split(mm,col(mm)),function(x){out <- t.test(x[1:15],x[16:25])$p.value}) # 1 2 #0.1091573 1.0000000 #or sapply(as.data.frame(mm), function(x) t.test(x[1:15],x[16:25])$p.value) # V1 V2 #0.1091573 1.0000000 A.K. On Saturday, February 15, 2014 3:19 PM, David Romano <drom...@stanford.edu> wrote: Hi folks, I'm having trouble with code that used to work, and I can't figure out what's going wrong. I'd be grateful for any help in sorting this out. Suppose I define a matrix > mm <- matrix(1:15, 25,2) and compare the first 15 values of column 1 of mm to the values remaining in the same column and obtain p values as follows: > c1 <- mm[,1] > out <- t.test(c1[1:15],c1[16:25]) ; out$p.value This of course works fine, but if I try to embed this line in a call to sapply to repeat this for each column, I get the following: > mm.pvals <- sapply(mm, function(x) {out <- t.test(x[1:15],x[16:25]) ; out$p.value}) Error in t.test.default(x[1:15], x[16:25]) : not enough 'x' observations What is baffling is code like this has worked for me before, and I can't tell what's triggering the error. Thanks in advance for your help! Best, David [[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.