Try this:

> x
   V1 V2 V3
1   1 15 34
2   1  4 66
3   1 24 65
4   2 23 47
5   2  9 36
6   3 58  9
7   3 38 64
8   3 12 64
9   3  4 15
10  4  1 88
11  4 23 90


x[tapply(seq(nrow(x)), x$V1, sample, 1),]


On Tue, Nov 9, 2010 at 9:01 PM, Achim Eberhart <
a.eberhart@pgrad.unimelb.edu.au> wrote:

> G'day R-helpers,
>
> I want to subsample rows of a large table based on the value in its first
> column. Of all rows sharing the same value in the first column I want to
> RANDOMLY extract only one.
> Thanks in advance,
>
> Achim
>
> example input
>
> 1       15      34
> 1       4       66
> 1       24      65
> 2       23      47
> 2       9       36
> 3       58      9
> 3       38      64
> 3       12      64
> 3       4       15
> 4       1       88
> 4       23      90
>
> desired output
>
> 1       4       66
> 2       23      47
> 3       12      64
> 4       1       88
>
> ______________________________________________
> R-help@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.
>



-- 
Henrique Dallazuanna
Curitiba-Paraná-Brasil
25° 25' 40" S 49° 16' 22" O

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