Hello everybody!
I have the following problem: I'd like to select a sample from a subsample
in a dataset. Actually, I don't want to select it, but to create a new
variable sampleNo that indicates to which sample (one or two) a case
belongs to.
Lets suppose I have a dataset containing 40 cases:
data <- data.frame(var1=seq(1:40), var2=seq(40,1))
The first sample (n=10) I drew like this:
data$sampleNo <- 0
idx <- sample(seq(1,nrow(data)), size=10, replace=F)
data[idx,]$sampleNo <- 1
Now, (and here my problems start) I'd like to draw a second sample (n=10).
But this sample should be drawn from the cases that don't belong to the
first sample only. *Additionally, "var1" should be an even number.*
So sampleNo should be 0 for cases that were not drawn at all, 1 for cases
that belong to the first sample and 2 for cases belonging to the second
sample (= sampleNo equals 0 and var1 is even).
I was trying to solve it like this:
idx2<-data$var1%%2 & data$sampleNo==0
sample(data[idx2,], size=10, replace=F)
But how can I set sampleNo to 2?
Thank you very much for your help!
David
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