[R] trouble using sapply to perform multiple t-test
arun
smartpink111 at yahoo.com
Sat Feb 15 22:39:27 CET 2014
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 <dromano at 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
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