[R] How can I extract part of the data with a selection criterion?

[Patrick Coulombe]

Hi,

Try ab[a==3,]

You're selecting only rows for which a==3 (before the comma), and all
columns (empty condition for column index, after the comma)

Patrick

2013/5/9 jpm miao <miaojpm at gmail.com>:
> Hi,
>
>    As an example, how can I get the data such that field a of ab, ab["a"],
> equals 3? I expect the answer to be the union of 2 and 4, as
>
>    Thanks,
>
>> a<-c(1,3,4,3,5,6,5)
>> b<-c(2,4,6,7,3,1,2)
>> ab<-data.frame(a,b)
>> ab
>   a b
> 1 1 2
> 2 3 4
> 3 4 6
> 4 3 7
> 5 5 3
> 6 6 1
> 7 5 2
>
>> ab[a==3]
> Error in `[.data.frame`(ab, a == 3) : undefined columns selected
>> ab[ab["a"]==3]
> [1] 3 3 4 7
>
>         [[alternative HTML version deleted]]
>
> ______________________________________________
> R-help at r-project.org mailing list
> https://stat.ethz.ch/mailman/listinfo/r-help
> PLEASE do read the posting guide http://www.R-project.org/posting-guide.html
> and provide commented, minimal, self-contained, reproducible code.