Hi,
you can try
df1<-split(df,df$groups)
lapply(df1, function(x)
{
x<-cbind(x,entry=0)
sam <- sample(x$plotno,1)
x$entry[which(x$plotno==sam)]<-"CONTROL"
x$entry[which(!x$plotno==sam)]<-"TEST"
x
}
)
Tanvir Ahamed
Göteborg, Sweden | mashra...@yahoo.com
________________________________
From: "DIGHE, NILESH [AG/2362]" <nilesh.di...@monsanto.com>
To: "r-help@r-project.org" <r-help@r-project.org>
Sent: Thursday, 17 March 2016, 18:18
Subject: [R] sample within a loop
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)
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PLEASE do read the posting guide http://www.R-project.org/posting-guide.html
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