[R] lapply with argument "X"

[Prof Brian Ripley]

On Wed, 6 Oct 2004 john.gavin at ubs.com wrote:

> Hi,
> 
> I am probably making a simple mistake but I can't see it
> 
> > X
> Error: Object "X" not found
> > exists("X")
> [1] FALSE
> > lapply("X", exists)
> [[1]]
> [1] TRUE
> 
> Why is lapply producing true?
> Is it something to do with the first
> argument of lapply also being called 'X'?

Yes.  Note that the first argument of lapply is supposed to be a list,
so what you are really using is

lapply(as.list("X"), exists)

and indeed an object named "X" exists in the environment within which 
exists() is run.

-- 
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