Question about type conversion in read.table with columns that contain "+" and "-" in R > 2.7

Somewhere in between the R-Versions 2.6 and 2.7 the behaviour of the function 
type.convert and therefore also read.table, read.csv, etc. has changed (see 
below):

In 2.6 and before:
type.convert(c("+", "-", "+"))
[1] + - +
Levels: + -

In 2.7 and later:
No, 2.7.0 only.
type.convert(c("+", "-", "+"))
[1] 0 0 0

Apparently, the character strings "+" and "-" are now interpreted as numeric 
and not any more as factors or character strings.

I have quite a number of files with columns that contain "+" or "-" and would 
like to convert these to characters or factors, without having to specify the 
individual column types manually.

Is there any way to still do so in a new version of R?
Even an old version of R (2.7.1)!

Please do note what the posting guide says about updating *before* 
posting, and using proper version numbers (there is no 'R 2.7')
Many thanks and best wishes,
Tim

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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

Question about type conversion in read.table with columns that contain "+" and "-" in R > 2.7

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