On 22 January 2021 at 21:35, Jens Heumann wrote:
| Dear r-devel,
|
| Today I came across what I would call inconsistencies in the `c.Date`
| method compared to what happens when concatenating other classes: 1.
| Non-commutativity: The type in the arrangements of the elements does
| matter (first element is critical), 2. the resulting value is numeric
| instead of expected integer (as in the case with factors).
|
| > ##
| Examples####################################################################
| > ## 1. Non-commutativity:
| > c(.1, Sys.Date())
| [1] 0.1 18649.0
| > c(as.integer(.1), Sys.Date())
| [1] 0 18649
| > ## whereas:
| > c(Sys.Date(), .1)
| Error in as.Date.numeric(e) : 'origin' must be supplied
| > c(Sys.Date(), as.integer(.1))
| Error in as.Date.numeric(e) : 'origin' must be supplied
| >
| > ## 2. Numeric instead of numeric value
| > str(c(as.integer(.1), Sys.Date()))
| num [1:2] 0 18649 ## not integer
| >
|
################################################################################
|
|
| I'm not sure if `c.Date` should redefined, since there would probably be
| many more classes to consider. However, the error message "'origin' must
| be supplied" cannot be served by the user and appears to me like an
| imperfection in the design.
|
| It would be desirable if `c.Date` harmonizes with the hierarchy stated
| in `?c`: "NULL < raw < logical < integer < double < complex < character
| < list < expression. [...] factors are treated only via their internal
| integer codes" and behaves best like a factor (and also throws integer
| values as in 2. above).
|
| Or maybe disabling non-dates at all `if (!all(sapply(list(Sys.Date(),
| .1), "class") == "Date")) stop...`, but this is a little beyond my
| knowledge.
|
| Anyway, I hope my remark is of relevance and contributes to the
| continuous development of our great programming language R!
Nice analysis, well done. Sadly it is also a "known feature" of the c()
operator and documented as such -- S3 class attributes drop. C'est la vie.
>From ?c
‘c’ is sometimes used for its side effect of removing attributes
except names, for example to turn an array into a vector.
‘as.vector’ is a more intuitive way to do this, but also drops
names. Note that methods other than the default are not required
to do this (and they will almost certainly preserve a class
attribute).
I have into that trap approximately 4.56e8 times in this idiom
> for (d in Sys.Date() + 0:2) print(d)
[1] 18649
[1] 18650
[1] 18651
>
Eventually one learns to switch to an iterator, and to pick the dates from a
vector preserving their class.
Dirk
--
https://dirk.eddelbuettel.com | @eddelbuettel | e...@debian.org
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