[R] selections of data by one variable

[Uwe Ligges]

Tu Yu-Kang wrote:

> 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.


Which language is this???

To summarize, all the code you specified is:

a<-c(1:10) & b<-c(11:20)
f<-d[d$b==17]
b==e<-c(13,15,17)

In R, each line for itself is syntacically completely incorrect (even if
you say something would work, which is definitely not the case)!
"PLEASE do read the posting guide!"

I guess you want something like

 d <- data.frame(a = 1:10, b = 11:20)
 subset(d, b == 17)
 e <- c(13, 15, 17)
 subset(d, b %in% e)

Uwe Ligges



> 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
> 
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