# sleep.paired <- merge(sleep[sleep$group==1,c(1,3)], sleep[sleep$group==2,c(1,3)], by="ID",sort=F)
# names(sleep.paired) <-c("ID","Drug1","Drug2")
"ID" "Drug1" "Drug2"
"1" "1" 0.7 1.9
"2" "2" -1.6 0.8
"3" "3" -0.2 1.1
"4" "4" -1.2 0.1
"5" "5" -0.1 -0.1
"6" "6" 3.4 4.4
"7" "7" 3.7 5.5
"8" "8" 0.8 1.6
"9" "9" 0 4.6
"10" "10" 2 3.4