I would change strategies. Create a new variable, say, num.in.grp <- rep(1:12, 4)
Then sample from 1:12, and add appropriate amounts so that they become row numbers within the four sets of 12 rows ctrls <- ssample(1:12, 4, replace=TRUE) + c(0,12,24,36) Now that we have four random row numbers, assign entry appropriately entry <- rep('TEST', 48) entry[ctrls] <- 'CONTROL' The above is not tested, and makes several assumptions, particularly that the data frame is sorted by groups and that there are four groups of 12 each. Thus it is does not generalize, not without some work. -Don -- Don MacQueen Lawrence Livermore National Laboratory 7000 East Ave., L-627 Livermore, CA 94550 925-423-1062 On 3/17/16, 10:18 AM, "R-help on behalf of DIGHE, NILESH [AG/2362]" <r-help-boun...@r-project.org on behalf of nilesh.di...@monsanto.com> wrote: >Dear R users, > My data frame has four "groups" namely A1, B2, C3, & D4. >Each group has 12 rows (variable "plotno). I like to randomly sample one >"plotno" within each "groups" variable and label it as "CONTROL" and >label others as "TEST" in a new variable called "entry". I am trying to >do this by looping over the group variable and then sample "plotno" >within a given group. I am ending up with four "CONTROL" plots but they >are generated by sampling over all the groups instead of each group. I >need one random "plotno" assigned as a "CONTROL" per group (A1, B2, C3, >D4). I would appreciate any help in modifying my function "funa" or >suggest any alternative and better way to do this task. Below is the >dataset and function I am working with. > ># dataset (df) >structure(list(plotno = 1:48, groups = c("A1", "A1", "A1", "A1", >"A1", "A1", "A1", "A1", "A1", "A1", "A1", "A1", "B2", "B2", "B2", >"B2", "B2", "B2", "B2", "B2", "B2", "B2", "B2", "B2", "C3", "C3", >"C3", "C3", "C3", "C3", "C3", "C3", "C3", "C3", "C3", "C3", "D4", >"D4", "D4", "D4", "D4", "D4", "D4", "D4", "D4", "D4", "D4", "D4" >)), .Names = c("plotno", "groups"), row.names = c(NA, -48L), class = >"data.frame") > ># function (funa) > >function (dataset) > >{ > > set.seed(1) > > bay <- unique(dataset$groups) > > IND <- c() > > df2 <- dataset > > for (i in bay) { > > IND[i] <- which(plotno %in% sample(plotno, 1)) > > df2$entry <- ifelse(df2$plotno %in% IND, "CONTROL", "TEST") > > } > > df2 > >} > > ># session info > >R version 3.2.1 (2015-06-18) > >Platform: i386-w64-mingw32/i386 (32-bit) > >Running under: Windows 7 x64 (build 7601) Service Pack 1 > > > >locale: > >[1] LC_COLLATE=English_United States.1252 LC_CTYPE=English_United >States.1252 LC_MONETARY=English_United States.1252 > >[4] LC_NUMERIC=C LC_TIME=English_United >States.1252 > > > >attached base packages: > >[1] stats graphics grDevices utils datasets methods base > > > >loaded via a namespace (and not attached): > >[1] tools_3.2.1 > >Thanks. >Nilesh > > >Nilesh Dighe >(806)-252-7492 (Cell) >(806)-741-2019 (Office) > > >This e-mail message may contain privileged and/or confidential >information, and is intended to be received only by persons entitled >to receive such information. If you have received this e-mail in error, >please notify the sender immediately. Please delete it and >all attachments from any servers, hard drives or any other media. Other >use of this e-mail by you is strictly prohibited. > >All e-mails and attachments sent and received are subject to monitoring, >reading and archival by Monsanto, including its >subsidiaries. The recipient of this e-mail is solely responsible for >checking for the presence of "Viruses" or other "Malware". >Monsanto, along with its subsidiaries, accepts no liability for any >damage caused by any such code transmitted by or accompanying >this e-mail or any attachment. > > >The information contained in this email may be subject to the export >control laws and regulations of the United States, potentially >including but not limited to the Export Administration Regulations (EAR) >and sanctions regulations issued by the U.S. Department of >Treasury, Office of Foreign Asset Controls (OFAC). As a recipient of >this information you are obligated to comply with all >applicable U.S. export laws and regulations. > > [[alternative HTML version deleted]] > >______________________________________________ >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.