On 04/12/2020 9:11 p.m., luke-tier...@uiowa.edu wrote:
On Sat, 5 Dec 2020, Duncan Murdoch wrote:
On 04/12/2020 2:26 p.m., luke-tier...@uiowa.edu wrote:
On Fri, 4 Dec 2020, Dénes Tóth wrote:
On 12/4/20 3:05 PM, Duncan Murdoch wrote:
...
It's tempting to suggest it should allow something like
mtcars |> subset(cyl == 4) |> lm(mpg ~ disp, data = .)
which would be expanded to something equivalent to the other versions:
but
that makes it quite a bit more complicated. (Maybe _ or \. should be
used
instead of ., since those are not legal variable names.)
I support the idea of using an underscore (_) as the placeholder symbol.
I strongly oppose adding a placeholder. Allowing for an optional
placeholder significantly complicates both implementing and explaining
the semantics. For a simple syntax transformation to be viable it
would also require some restrictions, such as only allowing a
placeholder as a top level argument and only once. Checking that these
restrictions are met, and accurately signaling when they are not with
reasonable error messages, is essentially an unsolvable problem given
R's semantics.
I don't think you read my suggestion, but that's okay: you're maintaining
it, not me.
I thought I did but maybe I missed something. You are right that
supporting a placeholder makes things a lot more complicated. For
being able to easily recognize the non-standard cases _ is better than
. but for me at least not by much.
We did try a number of variations; the code is in the R-syntax branch.
At the root of that branch are two .md files with some notes as of
around useR20. Once things settle down I may update those and look
into turning them into a blog post.
Thanks for pointing out those documents.
Duncan Murdoch
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