On 12-09-13 7:18 AM, Gian Maria Niccolò Benucci wrote:
Thank you very much for your help,
I was wondering if is possible to sample randomly specifying to select in a
particular group of data inside the matrix, for example only within the
whole samples collected in 2011 I would randomly choose 20 random samples...
You need two steps: find the rows that meet your condition, then sample
from those. For example,
rows <- which( a$year == 2011 )
sample(rows, 20)
There is one thing to watch out for: if you have a condition that only
matches one row, you will get unexpected results here, because the
sample will be taken from 1:rows. See the examples in ?sample for the
workaround that uses sample.int.
Duncan Murdoch
Thanks a again,
Gian
On 13 September 2012 12:26, anna freni sterrantino <annafr...@yahoo.it>wrote:
Hello Gian,
sure sample function
will do it for your sampling.
a=as.data.frame(matrix(1:20,4))
sample(rownames(a),2)
see ?sample for more details.
Hope it helps
Cheers
Anna
Anna Freni Sterrantino
Department of Statistics
University of Bologna, Italy
via Belle Arti 41, 40124 BO.
------------------------------
*Da:* Gian Maria Niccolò Benucci <gian.benu...@gmail.com>
*A:* r-help@r-project.org
*Inviato:* Giovedì 13 Settembre 2012 10:42
*Oggetto:* [R] random sampling inside a dataset
Hi all,
I am wondering if do exist a function in R that allow me to sample or
choose randomly the rows (i.e., samples) inside a given matrix.
Thank you very much in advance.
Cheers,
--
Gian
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