R help - Mar 2013 - Check if a character vector can be coerced to numeric?

Given an arbitrary set of character vectors:

myvect1 <- c("abc","3","4")
myvect2 <- c("2","3","4")

I would like to develop a function that will convert any vectors that can
be PROPERLY converted to a numeric (myvect2) into a numeric, but leaves
character vectors which cannot be converted (myvect1) alone.  Is there any
simple way to do this (e.g. some function that tests if a vector is
coercible to a numeric before doing so)?

--j

-- 
Jonathan A. Greenberg, PhD
Assistant Professor
Global Environmental Analysis and Remote Sensing (GEARS) Laboratory
Department of Geography and Geographic Information Science
University of Illinois at Urbana-Champaign
607 South Mathews Avenue, MC 150
Urbana, IL 61801
Phone: 217-300-1924
http://www.geog.illinois.edu/~jgrn/
AIM: jgrn307, MSN: jgrn307@hotmail.com, Gchat: jgrn307, Skype: jgrn3007

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On 21/03/2013 18:20, Jonathan Greenberg wrote:
> Given an arbitrary set of character vectors:
>
> myvect1 <- c("abc","3","4")
> myvect2 <- c("2","3","4")
>
> I would like to develop a function that will convert any vectors that can
> be PROPERLY converted to a numeric (myvect2) into a numeric, but leaves
> character vectors which cannot be converted (myvect1) alone.  Is there any
> simple way to do this (e.g. some function that tests if a vector is
> coercible to a numeric before doing so)?
>
> --j
?type.convert

It does depend what you mean by 'properly'.  Can 
"123.456789012344567890123455" be converted 'properly'?  [See
the NEWS
for 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

Using capital letters does not improve clarity... it just offends people.

Does read.table and friends not do this to your satisfaction already with
as.is=TRUE? If not, shouldn't coercing it and checking for NA serve?

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Jonathan Greenberg <jgrn at illinois.edu> wrote:
>Given an arbitrary set of character vectors:
>
>myvect1 <- c("abc","3","4")
>myvect2 <- c("2","3","4")
>
>I would like to develop a function that will convert any vectors that
>can
>be PROPERLY converted to a numeric (myvect2) into a numeric, but leaves
>character vectors which cannot be converted (myvect1) alone.  Is there
>any
>simple way to do this (e.g. some function that tests if a vector is
>coercible to a numeric before doing so)?
>
>--j