Re: [R] sampling problem - new to R

From: Sarah Goslee <sarah.goslee_at_gmail.com>
Date: Wed, 06 Jun 2007 09:29:00 -0400

Claire,

Here's one way to do it:

# first, generate some sample data to try
> treedata <- cbind.data.frame(Tree=1:25, Plot=sample(1:5, 25, replace=TRUE))
> treedata <- treedata[order(treedata$Plot),]
> treedata

   Tree Plot

1     1    1
2     2    1
6     6    1
9     9    1

11 11 1
17 17 1
18 18 1
23 23 1
13 13 2
16 16 2
25 25 2
5 5 3
10 10 3
4     4    4
7     7    4
8     8    4
24   24    4
3     3    5

12 12 5
14 14 5
15 15 5
19 19 5
20 20 5
21 21 5
22 22 5

# then randomly choose one tree from each plot # getting a different random set each time
> sapply(split(treedata$Tree, treedata$Plot), sample, 1)
 1 2 3 4 5
 2 25 10 4 21
> sapply(split(treedata$Tree, treedata$Plot), sample, 1)
 1 2 3 4 5
23 13 5 4 14

Hope that solves it for you,
Sarah

On 6/5/07, baldeck <cabaldeck_at_yahoo.com> wrote:
>
> I have a data set of individual trees and the plots that they are in:
>
> Tree Plot
> 56749 1
> 63494 1
> 87375 1
> 37494 2
> 92753 3
> 34847 3
> 38747 4 etc...
>
> So each plot is represented once for every individual that occurrs in it.
> Plots get different numbers of rows because there can be a different number
> of individuals in each plot.
>
> I want to make a data frame that consists of one individual from each plot.
> I would like to randomly choose one individual from each plot that is
> present in the data set. I will have to do this to multiple data sets which
> may contain different plots, and may contain up to 1200 plots, so I can't
> choose the plots by hand.
>
> Please help me with this. I'm an ecologist and I'm in Panama, with no one
> around who is educated in R. Whoever solves this problem for me will be
> acknowledged in any resulting publications.
>
> Thanks!
> -Claire
> --

-- 
Sarah Goslee
http://www.functionaldiversity.org

______________________________________________
R-help_at_stat.math.ethz.ch 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.
Received on Wed 06 Jun 2007 - 14:01:30 GMT

Archive maintained by Robert King, hosted by the discipline of statistics at the University of Newcastle, Australia.
Archive generated by hypermail 2.2.0, at Wed 06 Jun 2007 - 14:31:59 GMT.

Mailing list information is available at https://stat.ethz.ch/mailman/listinfo/r-help. Please read the posting guide before posting to the list.