Hi, I guess it is because when you have the FALSE option the sample function take off the number from the whole population so your data_frame becomes different in length. If you try with the option TRUE it works (of course) but then you have the possibility that you sample the same row twice. Hope this can help
On 4 October 2012 11:06, Gian Maria Niccolò Benucci <gian.benu...@gmail.com>wrote: > Hi again to everybody, > > I incountered the following error when I try to make a sample inside a > dataset. > My code is: > > > data_ostrya <- sample(ostrya,200, replace=F) > Error in `[.data.frame`(x, .Internal(sample(length(x), size, replace, : > cannot take a sample larger than the population when 'replace = FALSE' > > Why it does not work? > The whole dataset is composed of 536 rows and I just want to sample > randomly 200 of them... > > Thank you in advance, > > Gian > > > > > On 13 September 2012 14:01, Duncan Murdoch <murdoch.dun...@gmail.com> > wrote: > > > On 12-09-13 7:43 AM, Gian Maria Niccolò Benucci wrote: > > > >> Thank you Duncan, > >> > >> I got the result of sampling, but it gave me only the row numbers. Is it > >> possible to have the entire row with variables and other information? > >> Because I need to re-sample inside my matrix the whole rows in reason to > >> have 20 samples (i.e., rows) each year. > >> Thank you for your invaluable help! > >> > > > > Use those row numbers to index the dataframe or matrix, e.g. > > > > a[rows,] > > > > Duncan Murdoch > > > > > >> Gian > >> > >> > >> On 13 September 2012 13:32, Duncan Murdoch <murdoch.dun...@gmail.com> > >> wrote: > >> > >> On 12-09-13 7:18 AM, Gian Maria NiccolÅ 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 NiccolÅ Benucci <gian.benu...@gmail.com> > >>>>> *A:* r-help@r-project.org > >>>>> *Inviato:* GiovedÄ 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 > >>>>> > >>>>> [[alternative HTML version deleted]] > >>>>> > >>>>> ______________________________****________________ > >>>>> R-help@r-project.org mailing list > >>>>> https://stat.ethz.ch/mailman/****listinfo/r-help< > https://stat.ethz.ch/mailman/**listinfo/r-help> > >>>>> <https://stat.**ethz.ch/mailman/listinfo/r-**help< > https://stat.ethz.ch/mailman/listinfo/r-help> > >>>>> > > >>>>> > >>>>> PLEASE do read the posting guide > >>>>> http://www.R-project.org/****posting-guide.html< > http://www.R-project.org/**posting-guide.html> > >>>>> <http://www.**R-project.org/posting-guide.**html< > http://www.R-project.org/posting-guide.html> > >>>>> > > >>>>> <http://www.**r-project.org/**posting-guide.**html< > http://r-project.org/posting-guide.**html> > >>>>> <http://**www.r-project.org/posting-**guide.html< > http://www.r-project.org/posting-guide.html> > >>>>> > > >>>>> > >>>>> > >>>>>> > >>>>> and provide commented, minimal, self-contained, reproducible code. > >>>>> > >>>>> > >>>>> > >>>>> > >>>>> > >>>> > >>>> > >>>> This body part will be downloaded on demand. > >>>> > >>>> > >>>> > >>> > >> > >> > > > > [[alternative HTML version deleted]] > > > ______________________________________________ > 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. > > [[alternative HTML version deleted]]
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