Using derivatives with random smooths by individual

[gavinsimpson]

Discussed in #242

^{Originally posted by TSeuH December 6, 2023}
Hello,

I have been trying to get the first derivatives for each individual fit from the following model:

gam.smooth <- gam(TV ~ groupID +
s(time, by = groupID) +
s(time, animalID, bs = "fs", m = 1),
data = dataTV, method = "REML")

fdSmooth <- derivatives(gam.smooth, n = 1000, term = "s(time)", partial_match = TRUE)

I see a column "fs_var" in fdSmooth, and I was assuming it would contain "animalID", just like by_var contains "groupID". I thought I could get the first derivative for each animalID, but with this code, I only get the first derivative for each groupID, regardless of the animalID.

Would it be possible to have the derivatives by animalID without changing the GAM?

Thank you.