Welcome to the community!
If I understand you correctly, you want to fit a model based on the observations only in 1st and 2nd group. Is that right?
Then, the following is supposed to work with no problem:
g12 <- subset(x = d, subset = (grp %in% c("1", "2")))
glm(formula = (grp ~ surviva), family = binomial, data = g12)
Can you please give it a try?
If it doesn't solve your problem, can you please provide a REPRoducible EXample of your problem? It provides more specifics of your problem, and it helps others to understand what problem you are facing.
In case you don't know how to make a reprex, here's a great link:
A minimal reproducible example consists of the following items:
A minimal dataset, necessary to reproduce the issue
The minimal runnable code necessary to reproduce the issue, which can be run
on the given dataset, and including the necessary information on the used packages.
Let's quickly go over each one of these with examples:
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