R help - Aug 2006 - get() in sapply() in with()

Dear All,

applying some function within a with() function I wanted to use also
sapply() and get() to form a data.frame, but did not succede.
Below is a simplified example.
It is possible to use sapply() within a with() function, it is also
possible to use get() within a with() function, but when I try to use get
within sapply within with I arrive at "Error in get(x, envir, mode,
inherits) : variable "v5" was not found".
Is there a solution?

Thanks,
Heinz T?chler


## example
df1 <- data.frame(v5=16:20, v6=21:25, v7=I(letters[16:20]),
v8=letters[16:20])

with(df1, sapply(c('v5', 'v6'), get) ) ## Error, see next line
## Error in get(x, envir, mode, inherits) : variable "v5" was not
found

with(df1, sapply(list(v5, v6), mean) ) # does work
with(df1, get('v5') ) # does work

platform       i386-pc-mingw32                          
arch           i386                                     
os             mingw32                                  
system         i386, mingw32                            
status         Patched                                  
major          2                                        
minor          3.1                                      
year           2006                                     
month          07                                       
day            23                                       
svn rev        38687                                    
language       R                                        
version.string Version 2.3.1 Patched (2006-07-23 r38687)

On Thu, 3 Aug 2006, Heinz Tuechler wrote:
> Dear All,
>
> applying some function within a with() function I wanted to use also
> sapply() and get() to form a data.frame, but did not succede.
> Below is a simplified example.
> It is possible to use sapply() within a with() function, it is also
> possible to use get() within a with() function, but when I try to use get
> within sapply within with I arrive at "Error in get(x, envir, mode,
> inherits) : variable "v5" was not found".
> Is there a solution?
This isn't what you want to hear, but the solution is probably to not use 
get(). How to not use get() will depend on what your problem really is.
>
> ## example
> df1 <- data.frame(v5=16:20, v6=21:25, v7=I(letters[16:20]),
v8=letters[16:20])
>
> with(df1, sapply(c('v5', 'v6'), get) ) ## Error, see next
line
> ## Error in get(x, envir, mode, inherits) : variable "v5" was not
found
get() looks in the environment it was called from, which is the 
environment inside lapply(), whose parent is the environment of 
the base package. There is no "v5" there.
> with(df1, sapply(list(v5, v6), mean) ) # does work
This works because list(v5,v6) is evaluated in df1.
> with(df1, get('v5') ) # does work
This works because get() looks in the environment it was called from, 
which is df1.


 	-thomas

Thomas Lumley			Assoc. Professor, Biostatistics
tlumley at u.washington.edu	University of Washington, Seattle

Thank you, Thomas!
It helps a lot to know that something is impossible and that I have to look
for a different kind of solution.
Heinz

At 07:33 03.08.2006 -0700, Thomas Lumley wrote:
>On Thu, 3 Aug 2006, Heinz Tuechler wrote:
>
>> Dear All,
>>
>> applying some function within a with() function I wanted to use also
>> sapply() and get() to form a data.frame, but did not succede.
>> Below is a simplified example.
>> It is possible to use sapply() within a with() function, it is also
>> possible to use get() within a with() function, but when I try to use
get
>> within sapply within with I arrive at "Error in get(x, envir,
mode,
>> inherits) : variable "v5" was not found".
>> Is there a solution?
>
>This isn't what you want to hear, but the solution is probably to not
use
>get(). How to not use get() will depend on what your problem really is.
>
>>
>> ## example
>> df1 <- data.frame(v5=16:20, v6=21:25, v7=I(letters[16:20]),
v8=letters[16:20])
>>
>> with(df1, sapply(c('v5', 'v6'), get) ) ## Error, see
next line
>> ## Error in get(x, envir, mode, inherits) : variable "v5" was
not found
>
>get() looks in the environment it was called from, which is the 
>environment inside lapply(), whose parent is the environment of 
>the base package. There is no "v5" there.
>
>> with(df1, sapply(list(v5, v6), mean) ) # does work
>
>This works because list(v5,v6) is evaluated in df1.
>
>> with(df1, get('v5') ) # does work
>
>This works because get() looks in the environment it was called from, 
>which is df1.
>
>
> 	-thomas
>
>Thomas Lumley			Assoc. Professor, Biostatistics
>tlumley at u.washington.edu	University of Washington, Seattle
>
>