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$p.valueThis of course works fine, but if I try to embed this line in a call to sapply to repeat this for each column, I get the following:> mm.pvals <- sapply(mm, function(x) {out <- t.test(x[1:15],x[16:25]) ;out$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]]
On 02/16/2014 07:16 AM, David Romano 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. >Hi David, You have here the old "s" problem. I suspect that you previously ran this code on a data frame, not a matrix. Try this: mm.pvals<-apply(mm,2, function(x) {out <- t.test(x[1:15],x[16:25]);out$p.value}) Jim
Hi David,
Try:
Check the output of:
lapply(mm,function(x) x) #mm is matrix
#and
lapply(as.data.frame(mm),function(x) x)
? sapply(split(mm,col(mm)),function(x){out <-
t.test(x[1:15],x[16:25])$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
??? [[alternative HTML version deleted]]
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