tl;dr:
Why are named arguments discouraged in `[.data.frame`, `[<-.data.frame` and
`[[.data.frame`?
(because this question is of the kind 'why is R designed like this?', I though
R-devel would be more appropriate than R-help)
#############################
Background:
Now and then students presents there fancy functions like this:
myfancyfun(d,12,0.3,0.2,500,1000,FALSE,TRUE,FALSE,TRUE,FALSE)
Incomprehensible. Thus, I encourage them to use spaces and name arguments, _at
least_ when trying to communicate their code with others. Something like:
myfancyfun(data = d, n = 12, gamma = 0.3, prob = 0.2,
size = 500, niter = 1000, model = FALSE,
scale = TRUE, drop = FALSE, plot = TRUE, save = FALSE)
Then some overzealous students started to use named arguments everywhere.
E-v-e-r-y-w-h-e-r-e. Even in the most basic situation when indexing vectors (as
a subtle protest?), like:
vec <- 1:9
vec[i = 4]
`[`(x = vec, i = 4)
vec[[i = 4]]
`[[`(x = vec, i = 4)
vec[i = 4] <- 10
`[<-`(x = vec, i = 4, value = 10)
...or when indexing matrices:
m <- matrix(vec, ncol = 3)
m[i = 2, j = 2]
`[`(x = m, i = 2, j = 2)
# 5
m[i = 2, j = 2] <- 0
`[<-`(x = m, i = 2, j = 2, value = 0)
######
This practice indeed feels like overkill, but it didn't seem to hurt either.
Until they used it on data frames. Then suddenly warnings appeared that named
arguments are discouraged:
d <- data.frame(m)
d[[i = "X2"]]
# [1] 4 5 6
# Warning message:
# In `[[.data.frame`(d, i = "X2") :
# named arguments other than 'exact' are discouraged
d[i = 2, j = 2]
# [1] 0
# Warning message:
# In `[.data.frame`(d, i = 2, j = 2) :
# named arguments other than 'drop' are discouraged
d[i = 2, j = 2] <- 5
# Warning message:
# In `[<-.data.frame`(`*tmp*`, i = 2, j = 2, value = 5) :
# named arguments are discouraged
##################################
Of course I could tell them "don't do it, it's overkill and not common
practice" or "it's just a warning, don't worry". However, I assume the warnings
are there for a good reason.
So how do I explain to the students that named arguments are actively
discouraged in `[.data.frame` and `[<-.data.frame`, but not in `[` and `[<-`?
When will they get bitten?
______________________________________________
R-devel@r-project.org mailing list
https://stat.ethz.ch/mailman/listinfo/r-devel
