[R] selections of data by one variable

[Tu Yu-Kang]

Dear R experts,

My problem is as follows:

Suppose I have a data frame d comprising two variable a<-c(1:10) & 
b<-c(11:20).

I now want to select a subgroup according the values of b.

I know if I just want to select, say, b=17, I can use f<-d[d$b==17] and R 
will give me 

> f
  a  b
7 7 17

However, if now I want to select a subgroup according to b==e<-c(13,15,17), 
then the same syntx doesn't work.

What is the correct way to do it?  My data have more than one million 
subjects, and I want to select part of them according to their id numbers.

Your help will be highly appreciated.

Best regards,

Yu-Kang