Exercise from last week

                     dat <- read.table(

                               'http://www.mpimg-berlin-dahlem.mpg.de/~rodent/ttable1',

                               fill=T, header=T, as.is=T

                     )

                     str(dat)

                     dat[dat$C57BL.6 != dat$C3H,]

                     dat[dat$C57BL.6 != dat$C3H,c(1,10,13)]