# Re: [R] selections of data by one variable

From: Uwe Ligges <ligges_at_statistik.uni-dortmund.de>
Date: Wed 04 May 2005 - 23:27:58 EST

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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