xg<- read.table(text="
x group
a 1
a 1
a 2
b 1
b 2
c 1
c 1
c 1
c 1
c 1
d 1
d 1
f 2
f 2",header=T)
xg1 <- xg$x[xg$group==1];xg1
b <- as.data.frame(table(xg1))
b <- b[order(-b$Freq,b$xg1),]
又回到那个交叉表了。。。想想!