mengchen <br /> a <- read.table(textConnection("a 1<br /> a 3<br /> a 9<br /> b 2<br /> b 4<br /> b 7<br /> c 6<br /> c 5"))</p> <p># method 1<br /> a[!duplicated(a$V1), ]<br /> # method 2<br /> tapply(a$V2, a$V1, "[", 1)<br /> </p>
