a=c("t","t","r","t","f","r","t","t","f")
b=c(1:9)
c=c(11:19)
d=data.table(a,b,c)d
a b c
t 1 11
t 2 12
r 3 13
t 4 14
f 5 15
r 6 16
t 7 17
t 8 18
f 9 19



第一步：d[b!=2]   删除b=2行
第二步：d[(a=="f" & b>4) | a=="r"), c:=3*c]

如何用一行完成以上两步？