ksmooth function doesn't work with parameters via ellipsis - r

Question

I am currently working with R due to a course at university, so I am still quite inexperienced.
We use R for exploratory data analysis. In a data analysis we are supposed to apply different regression models to the data and generate the same plots for each. Additionally, we are supposed to play a bit with the parameters for learning purposes. To avoid unattractive 10-20 times copy-pasting I wrote a function that shows the regression function and the parameters for it as an ellipsis (...). In this function I call the passed function with the ellipsis as parameter.
library("astsa")
data_glob <- globtemp
plot.data.and.reg <- function(data, reg.func, ...){
model <- reg.func(...)
par(mfrow = c(1, 2))
plot(data)
abline(model, col = "orange", lwd = 3)
qqnorm(data)
}
This works for the simple lm function, but unfortunately not for the ksmooth function.
When I pass this function I get the error message: "numeric y must be supplied. For density estimation use density()".
plot.data.and.reg(
data_g,
lm,
list(
formula = as.formula("data_glob ~ time(data_glob)"),
data = data_glob
)
)
plot.data.and.reg(
data_glob,
ksmooth,
list(
x = as.numeric(time(data_glob)),
y = as.numeric(data_glob),
kernel = "box",
bandwidth = 0.25
)
)
Thereupon I looked at the source code of ksmooth. It shows that this error message occurs because the check "missing(y)" fails. Apparently a problem occurs because I passed the parameters as an ellipsis and it doesn't seem to "unpack".
For simplicity, I wrote a dummy function to test if I can add this "unpack" myself.
test.wrapper <- function(func, ...){
func(...)
}
test <- function(x, y){
match.call()
if(missing(y))
print("Leider hatte ich Recht")
print(x)
print(y)
}
test.wrapper(test, list(x = 10, y = 20))
Unfortunately I have not found a solution yet.
From Python I know it so that as with kwargs a dictionary can be unpacked with the ** operator. Is there an equivalent in R? Or how to make sure in R that the parameters from the ellipsis are used correctly?
Since it worked with the lm function without errors I also looked again in their source code . Unfortunately, with my little experience in R, I can't see exactly where the essential difference is.
Overall, I would attribute the error to the fact that the ksmooth function is not yet designed for use with an ellipsis, but I am not sure. How would I need to adjust the ksmooth code to make it work with ...?
(For my Uni task, I will resort to the copy-paste (anti) pattern if in doubt. After searching for so long, I would still be interested in the solution and it may be useful in the future).
Thanks a lot for your help!

Answer 1

The closest equivalent of the */** splat in Python is the do.call function.
However, you don’t need this here. The actual issue is that you’re passing the extra arguments as a list rather than individually. Once you flatten the list, it works1:
plot.data.and.reg(
data_glob,
ksmooth,
x = as.numeric(time(data_glob)),
y = as.numeric(data_glob),
kernel = "box",
bandwidth = 0.25
)
I’m actually surprised that it works with a list for lm; that’s not intentional, it’s essentially an accident caused by how lm is currently implemented.
1 I say it “works” because there’s no error and it plots something, but with your example data there’s no visible regression line (abline is inappropriate for the output of ksmooth), and the smoothing parameters do nothing — the result is identical to the unsmoothed input.
To get this to work, use lines instead of abline. And as for the smoothing, for your example data a bandwidth of 10 works fine.