Hi Rui , I tried that one before I send out my original message. it gave me only this,
tapply(tab$S1, tab$time, function(x) length(unique(x))) 1 2 3 2 1 3 I am expecting an output of like this time S1 1 2 2 1 3 3 On Sat, Nov 21, 2015 at 2:38 PM, <ruipbarra...@sapo.pt> wrote: > Hello, > > Try > > tapply(tab$S1, tab$time, function(x) length(unique(x))) > > Hope this helps, > > Rui Barradas > > > Citando Ashta <sewa...@gmail.com>: > > Hi Bert and all, > I have related question. In each time period there were different > locations where the samples were collected (S1). I want count the > number of unique locations (S1) for each unique time period . So in > time 1 the samples were collected from two locations and time 2 only > from one location and time 3 from three locations.. > > tab <- read.table(textConnection(" time S1 rep > 1 1 1 > 1 2 1 > 1 2 2 > 2 1 1 > 2 1 2 > 2 1 3 > 2 1 4 > 3 1 1 > 3 2 1 > 3 3 1 "),header = TRUE) > > what I want is > > time S1 > 1 2 > 2 1 > 3 3 > > Thank you again. > > > > On Sat, Nov 21, 2015 at 1:30 PM, Ashta <sewa...@gmail.com> wrote: > > Thank you Bert! > > What I want is at least 500 samples based on random sampling of time > period. This allows samples collected at the same time period are > included together. > > Your script is doing what I wanted to do!! > > Many thanks > > > > > On Sat, Nov 21, 2015 at 1:15 PM, Bert Gunter <bgunter.4...@gmail.com> wrote: > > David's "solution" is incorrect. It can also fail to give you times > with a total of 500 items to sample from in the time periods. > > It is not entirely clear what you want. The solution below gives you a > random sample of time periods in which X1>0 and the total number of > samples among them is >= 500. It does not give you the fewest number > of periods that can do this. Is this what you want? > > tab[with(tab,{ > rownums<- sample(seq_len(nrow(tab))[X1>0]) > sz <- cumsum(X2[rownums]) > rownums[c(TRUE,sz<500)] > }),] > > Cheers, > Bert > > > Bert Gunter > > "Data is not information. Information is not knowledge. And knowledge > is certainly not wisdom." > -- Clifford Stoll > > > On Sat, Nov 21, 2015 at 10:56 AM, Ashta <sewa...@gmail.com> wrote: > > Thank you David! > > I rerun the your script and it is giving me the first three time periods > is it doing random sampling? > > tab.fan > time X1 X2 > 2 2 5 230 > 3 3 1 300 > 5 5 2 10 > > > > On Sat, Nov 21, 2015 at 12:20 PM, David L Carlson <dcarl...@tamu.edu> wrote: > > Use dput() to send data to the list as it is more compact: > > dput(tab) > > structure(list(time = 1:8, X1 = c(0L, 5L, 1L, 0L, 2L, 3L, 1L, > 4L), X2 = c(251L, 230L, 300L, 25L, 10L, 101L, 300L, 185L)), .Names = > c("time", > "X1", "X2"), class = "data.frame", row.names = c(NA, -8L)) > > You can just remove the lines with X1 = 0 since you don't want to use them. > > tab.sub <- tab[tab$X1>0, ] > > Then the following gives you a sample: > > tab.sub[cumsum(sample(tab.sub$X2))<=500, ] > > Note, that your "solution" of times 6, 7, and 8 will never appear because > the sum of the values is 586. > > > David L. Carlson > Department of Anthropology > Texas A&M University > > -----Original Message----- > From: R-help [mailto:r-help-boun...@r-project.org] On Behalf Of Ashta > Sent: Saturday, November 21, 2015 11:53 AM > To: R help <r-help@r-project.org> > Subject: [R] Conditional Random selection > > Hi all, > > I have a data set that contains samples collected over time. In > each time period the total number of samples are given (X2) The goal > is to select 500 random samples. The selection should be based on > time (select time periods until I reach 500 samples). Also the time > period should have greater than 0 for X1 variable. X1 is an indicator > variable. > > Select "time" until reaching the sum of X2 is > 500 and if X1 is > 0 > > tab <- read.table(textConnection(" time X1 X2 > 1 0 251 > 2 5 230 > 3 1 300 > 4 0 25 > 5 2 10 > 6 3 101 > 7 1 300 > 8 4 185 "),header = TRUE) > > In the above example, samples from time 1 and 4 will not be selected > ( X1 is zero) > So I could reach my target by selecting time 6,7, and 8 or time 2 and > 3 and so on. > > Can any one help to do that? > > ______________________________________________ > R-help@r-project.org mailing list -- To UNSUBSCRIBE and more, see > 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@r-project.org mailing list -- To UNSUBSCRIBE and more, see > 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@r-project.org mailing list -- To UNSUBSCRIBE and more, see > https://stat.ethz.ch/mailman/listinfo/r-help > PLEASE do read the posting guide > http://www.R-project.org/posting-guide.htmland provide commented, minimal, > self-contained, reproducible code. > > > ______________________________________________ R-help@r-project.org mailing list -- To UNSUBSCRIBE and more, see 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.