sapply behavior
Elizabeth Purdom wrote:
I use sapply very frequently, but I have recently noticed a behavior of sapply which I don't understand and have never seen before. Basically, sapply returns what looks like a matrix, says it a matrix, and appears to let me do matrix things (like transpose). But it is also a list and behaves like a list when I subset it, not a vector (so I can't sort a row for instance). I don't know where this is coming from so as to avoid it, nor how to handle the beast that sapply is returning. I double checked my old version of R and apparently this same thing happens in 1.8.0, though I never experienced it. I had a hard time reproducing it, and I don't know what's setting it off, but the code below seems to do it for me. (I'm using R on Windows XP, either 1.8.0 or 1.9.1) Thanks for any help, Elizabeth Purdom
> temp2<-matrix(sample(1:6,6,replace=F),byrow=F,nrow=6,ncol=4)
> colnames(temp2)<-paste("A",as.character(1:4),sep="")
> temp2<-as.data.frame(temp2)
It is this coercion to the data frame that is injecting a list-like property into the result. Try your script without that line and it will work as you expect.
> newtemp2<-sapply((1:6),function(x){xmat<-temp2[temp2[,1]==x,,drop=F];return(xmat[1,])})
> print(newtemp2) #looks like matrix
[,1] [,2] [,3] [,4] [,5] [,6] A1 1 2 3 4 5 6 A2 1 2 3 4 5 6 A3 1 2 3 4 5 6 A4 1 2 3 4 5 6
The best thing to do in a situation like this is to use the str function to see the details of the structure of the object.