R help - Oct 2004 - lapply with argument "X"

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'?
> version
         _              
platform i386-pc-mingw32
arch     i386           
os       mingw32        
system   i386, mingw32  
status                  
major    2              
minor    0.0            
year     2004           
month    10             
day      04             
language R                  

Regards,

John.

John Gavin <john.gavin at ubs.com>,
Quantitative Risk Models and Statistics,
UBS Investment Bank, 6th floor, 
100 Liverpool St., London EC2M 2RH, UK.
Phone +44 (0) 207 567 4289
Fax   +44 (0) 207 568 5352

Visit our website at http://www.ubs.com

This message contains confidential information and is intend...{{dropped}}

<john.gavin at ubs.com> writes:
> 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'?
Internal variable capture. I think this is a bug.

Also, try  lapply("FUN",get)


-- 
   O__  ---- Peter Dalgaard             Blegdamsvej 3  
  c/ /'_ --- Dept. of Biostatistics     2200 Cph. N   
 (*) \(*) -- University of Copenhagen   Denmark      Ph: (+45) 35327918
~~~~~~~~~~ - (p.dalgaard at biostat.ku.dk)             FAX: (+45) 35327907

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

Hi,
> From: Peter Dalgaard [mailto:p.dalgaard at biostat.ku.dk]
> <john.gavin at ubs.com> writes:
> 
> > 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'?
> 
> Internal variable capture. I think this is a bug.
Fyi, I wanted to show that users have to use single
character variables with caution because of the existance
of objects like 'c', 'q', 'T' and 'F'.
So I tried to say
> xx <- c(letters, LETTERS) ; xx[sapply(xx, exists)]
 [1] "c" "q" "t" "C" "D"
"F" "I" "Q" "T" "X"

but the appearance of 'X' undermines my code.
In that sense, it seems like a bug to me.
(I have a local definition for 'Q' - quit without asking.)
> Also, try  lapply("FUN",get)
Agreed.

Regards,

John.

John Gavin <john.gavin at ubs.com>,
Quantitative Risk Models and Statistics,
UBS Investment Bank, 6th floor, 
100 Liverpool St., London EC2M 2RH, UK.
Phone +44 (0) 207 567 4289
Fax   +44 (0) 207 568 5352

> -----Original Message-----
> From: Peter Dalgaard [mailto:p.dalgaard at biostat.ku.dk]
> Sent: 06 October 2004 17:31
> To: Gavin, John
> Cc: r-help at stat.math.ethz.ch
> Subject: Re: [R] lapply with argument "X"
> 
> 
> <john.gavin at ubs.com> writes:
> 
> > 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'?
> 
> Internal variable capture. I think this is a bug.
> 
> Also, try  lapply("FUN",get)
> 
Visit our website at http://www.ubs.com

This message contains confidential information and is intend...{{dropped}}