Inconsistent messages with [[ list indexing (PR#359)

[ripley@stats.ox.ac.uk]

R 0.90.0:

> Empl <- list(aa=1, b=2, c=3)
> Empl[[as.numeric(NA)]]
Error in Empl[[as.numeric(NA)]] : subscript out of bounds
> Empl[[as.integer(NA)]]
Error: attempt to select more than one element
> Empl[[as.logical(NA)]]
Error: attempt to select more than one element

Now,

(a) None of those messages is appropriate.

(b) At least the first two should be the same.

(c) S gives NULL in each case.

Is there any reason not to follow S here?  If so, I would prefer a
specific error message (`NA cannot be used to select a list element').

The usage

Empl[[ match("a", names(Empl)) ]]

is a very convenient one to defeat partial matching, but the current
behaviour of R defeats it. OK,

Empl[ match("a", names(Empl)) ] [[1]]

works, but this is an ugly hack (and the answer should I believe be the
same as [[ ]]).

-- 
Brian D. Ripley,                  ripley@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 272860 (secr)
Oxford OX1 3TG, UK                Fax:  +44 1865 272595


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