[Rd] pmin() and pmax() should process a single list of vectors, rather than returning it

[Sebastian Martin Krantz]

Dear R Core,

The {kit} package has a nice set of parallel statistical functions
complimenting base R's pmin() and pmax(): psum(), pprod(), pmean(), etc..
These can be called on a set of vectors like pmin() and pmax() e.g.
with(mtcars,  psum(mpg, carb, wt)) or on a single list of vectors e.g.
psum(mtcars). In contrast, pmin() and pmax() only allow the former. Calling
pmax(mtcars) oddly returns mtcars as is, without giving any error or
warning. I think this behavior should be changed to come in line with the
kit versions.

kit::psum is defined as:
psum <- function(..., na.rm=FALSE) .Call(CpsumR,  na.rm, if (...length() ==
1L && is.list(..1)) ..1 else list(...))

The first line of pmin() and pmax() is elts <- list(...). I propose
changing that first line to:
elts <- if (...length() == 1L && is.list(..1)) unclass(..1) else list(...).

This will provide convenient functionality (do.call(pmax, mtcars) is
inconvenient), and guard against the (odd) behavior of simply returning a
list passed to these functions.

Best regards,

Sebastian Krantz

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