There's a funny inconsistency in how t.test handles paired=T or paired=F. If x and y parameters are lists, paired=F works, but paired=T doesn't.
> lg=read.csv("my.csv") > a = subset(lg, condition=="a")["score"] > b = subset(lg, condition=="b")["score"] > t.test(a,b) > t.test(a,b, paired=TRUE) Error in `[.data.frame`(y, yok) : undefined columns selected But this works > a=a[,1] > b=b[,1] > t.test(a,b, paired=TRUE) ... ______________________________________________ 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.