[R] random section of samples based on group membership
Hi all, I have a matrix of 474 rows (samples) with 565 columns (variables). each of the 474 samples belong to one of 120 groups, with the groupings as a column in the above matrix. For example, the group column would be: 1 1 1 2 2 2 . . . 120 120 I want to randomly select one from each group. Not all the groups have the same number of samples, some have 4, some 3 etc. Is there a function to do this, or would I need to write a looping statement to look at each successive group? I basically want to combine the randomly selected samples from the 120 groups into a new matrix in order to perform a cluster analysis. Thanks, Wade __ R-help@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.
Re: [R] random section of samples based on group membership
Dear Wade, Say that your groups are groups - sort(sample(1:10, 100, replace = TRUE)) Create a dummy rows - 1:length(groups) Then tapply( rows, groups, function(x) sample(x, 1)) does the trick to select the row numbers you need for your sampling. Sincerely, Carlos J. Gil Bellosta http://www.datanalytics.com http://www.data-mining-blog.com Quoting Wade Wall [EMAIL PROTECTED]: Hi all, I have a matrix of 474 rows (samples) with 565 columns (variables). each of the 474 samples belong to one of 120 groups, with the groupings as a column in the above matrix. For example, the group column would be: 1 1 1 2 2 2 . . . 120 120 I want to randomly select one from each group. Not all the groups have the same number of samples, some have 4, some 3 etc. Is there a function to do this, or would I need to write a looping statement to look at each successive group? I basically want to combine the randomly selected samples from the 120 groups into a new matrix in order to perform a cluster analysis. Thanks, Wade __ R-help@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. __ R-help@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.
Re: [R] random section of samples based on group membership
Well, how you do it might be a matter of taste with respect to how you
want the results.
You could try using by with sample
by(x,x[,3],function(y){y[sample(nrow(y),1),]})
This will return a list with one list element for each sample group.
You can the combine the list back into a matrix.
That's my naive solution; no doubt there will be half a dozen better
ways to go about it.
Also, some of the clustering functions I have seen will sample for you.
On 7/24/06, Wade Wall [EMAIL PROTECTED] wrote:
Hi all,
I have a matrix of 474 rows (samples) with 565 columns (variables).
each of the 474 samples belong to one of 120 groups, with the
groupings as a column in the above matrix. For example, the group
column would be:
1
1
1
2
2
2
.
.
.
120
120
I want to randomly select one from each group. Not all the groups
have the same number of samples, some have 4, some 3 etc. Is there a
function to do this, or would I need to write a looping statement to
look at each successive group?
I basically want to combine the randomly selected samples from the 120
groups into a new matrix in order to perform a cluster analysis.
Thanks,
Wade
__
R-help@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.
--
Regards,
Mike Nielsen
__
R-help@stat.math.ethz.ch mailing list
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PLEASE do read the posting guide http://www.R-project.org/posting-guide.html
and provide commented, minimal, self-contained, reproducible code.
Re: [R] random section of samples based on group membership
On Mon, 24 Jul 2006 11:18:10 -0400,
Wade Wall [EMAIL PROTECTED] wrote:
Hi all, I have a matrix of 474 rows (samples) with 565 columns
(variables). each of the 474 samples belong to one of 120 groups, with
the groupings as a column in the above matrix. For example, the group
column would be:
1 1 1 2 2 2 . . . 120 120
I want to randomly select one from each group. Not all the groups have
the same number of samples, some have 4, some 3 etc. Is there a
function to do this, or would I need to write a looping statement to
look at each successive group?
I use the following for that (some of it hacked from help(sample)):
.resample - function(x, size, ...) {
if(length(x) = 1) {
if(!missing(size) size == 0) x[FALSE] else x
} else sample(x, size, ...)
}
randpick - function(x, by, size = 1, ...)
{
nx - seq(nrow(x))
ind - unlist(tapply(nx, by, .resample, size, ...))
x[nx %in% ind, ]
}
So, for instance:
R randpick(Indometh, Indometh$Subject, 3)
Subject time conc
21 0.50 0.94
71 3.00 0.12
11 1 8.00 0.05
15 2 1.00 0.70
16 2 1.25 0.64
19 2 4.00 0.20
25 3 0.75 1.16
29 3 3.00 0.22
32 3 6.00 0.08
34 4 0.25 1.85
43 4 6.00 0.07
44 4 8.00 0.07
48 5 1.00 0.39
54 5 6.00 0.10
55 5 8.00 0.06
58 6 0.75 1.03
64 6 5.00 0.13
65 6 6.00 0.10
R randpick(Indometh, Indometh$Subject, 2)
Subject time conc
81 4.00 0.11
10 1 6.00 0.07
14 2 0.75 0.71
20 2 5.00 0.25
23 3 0.25 2.72
28 3 2.00 0.39
39 4 2.00 0.40
43 4 6.00 0.07
48 5 1.00 0.39
52 5 4.00 0.11
57 6 0.50 1.44
66 6 8.00 0.09
The 'by' argument allows to sample within any combination of factors
desired.
Cheers,
--
Seb
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