[Rd] html help fails for named vector objects (PR#9927)

[Prof Brian Ripley]

On a normal R help system any version of help(letters) tries to give you 
help on a, b, etc.  This is intentional (although the documentation is 
unclearly worded), and has been the case since at least R 2.0.0.
Some versions of help will display only the first topic.

If help(letters, htmlhelp=FALSE) does something else on your system, that 
is a MacOS-specific bug since the topic selected should not depend on the 
optional arguments.

What is unclear from the documentation is what should happen with

help(c("help", "help.search"))

It seems that for text help you get the first, for htmlhelp both.

There are two things we could do to help (apart from clarifying the 
documentation):

1) If 'topic' is neither a name nor a character vector (e.g. an expression 
like the last example) give an explicit error.

2) if topic is a character vector of length > 1, use the name.


On Sun, 23 Sep 2007, John.Maindonald at anu.edu.au wrote:

>   help(letters, htmlhelp=TRUE) fails.
>
> Under the Mac OSX gui, the message is 'Help for the topic "a" was not
> found.' Under the version documented below, and under Windows, the
> message is
>
>   "No documentation for 'a' in specified packages and libraries:"
> repeated for all the elements of letters, then followed by
>   "you could try 'help.search("a")'",
> again repeated for all elements of letters.
>
> The outcome seems similar for any character vector (including matrix)
> object, e.g. the matrix 'primateDNA' in the DAAGbio package.
>
> The following have the expected result
>   help("letters", htmlhelp=TRUE)
>   help(letters, htmlhelp=FALSE)

But the documented and actual results are the same, and different in the 
two cases.

> The same result is obtained with R-2.5.1.
>
>
> --please do not edit the information below--
>
> Version:
> platform = i386-apple-darwin8.10.1
> arch = i386
> os = darwin8.10.1
> system = i386, darwin8.10.1
> status = beta
> major = 2
> minor = 6.0
> year = 2007
> month = 09
> day = 22
> svn rev = 42941
> language = R
> version.string = R version 2.6.0 beta (2007-09-22 r42941)
>
> Locale:
> C
>
> Search Path:
> .GlobalEnv, package:testpkg, package:stats, package:graphics,
> package:grDevices, package:utils, package:datasets, package:methods,
> Autoloads, package:base
>
> John Maindonald             email: john.maindonald at anu.edu.au
> phone : +61 2 (6125)3473    fax  : +61 2(6125)5549
> Centre for Mathematics & Its Applications, Room 1194,
> John Dedman Mathematical Sciences Building (Building 27)
> Australian National University, Canberra ACT 0200.
>
> ______________________________________________
> R-devel at r-project.org mailing list
> https://stat.ethz.ch/mailman/listinfo/r-devel
>

-- 
Brian D. Ripley,                  ripley at stats.ox.ac.uk
Professor of Applied Statistics,  http://www.stats.ox.ac.uk/~ripley/
University of Oxford,             Tel:  +44 1865 272861 (self)
1 South Parks Road,                     +44 1865 272866 (PA)
Oxford OX1 3TG, UK                Fax:  +44 1865 272595