R help - Oct 2008 - getting the "name" of an object

Hello,

I'm looking for a way to get the "name" of an object when it is
used
within an "sapply".

More precisely, with a simple example :

I have a named list of objects :

myList = list(a=rnorm(10),b=rnorm(10),c=rnorm(10))

I would like to create a new object from each of the components of
myList using the "sapply" function, for example to get the mean of all
components of myList :

createVarMean = function(obj){

      obj.name = ******
      obj.mean = mean(obj)
      assign(obj.name,obj.mean)

}#end of createVarMean

Using :

sapply(myList,createVarMean)

Should then create all the objects.

Any idea to get the names ? Perhaps using object oriented programming
(is there an equivalent of the "this" syntax of Java in R ?) ?

I don't want to use a loop here.

thank you for your time and trouble,

Fran?ois.

On 10/22/2008 10:02 AM, francois Guilhaumon wrote:
> Hello,
> 
> I'm looking for a way to get the "name" of an object when it
is used
> within an "sapply".
> 
> More precisely, with a simple example :
> 
> I have a named list of objects :
> 
> myList = list(a=rnorm(10),b=rnorm(10),c=rnorm(10))
> 
> I would like to create a new object from each of the components of
> myList using the "sapply" function, for example to get the mean
of all
> components of myList :
> 
> createVarMean = function(obj){
> 
>       obj.name = ******
>       obj.mean = mean(obj)
>       assign(obj.name,obj.mean)
> 
> }#end of createVarMean
sapply doesn't pass the names in, but there are other choices:

sapply(seq_along(myList), function(i) list(obj.name=names(myList)[i], 
obj.mean = mean(myList[[i]])))

which iterates over the indices of myList, rather than over the elements 
of it.  But a simple sapply(myList, function(obj) mean(obj)) is probably 
preferable, since it attaches the names in a nice way:

 > sapply(myList, function(obj) mean(obj))
          a          b          c
-0.4097454 -0.5057526 -0.2204035
> Using :
> 
> sapply(myList,createVarMean)
> 
> Should then create all the objects.
> 
> Any idea to get the names ? Perhaps using object oriented programming
> (is there an equivalent of the "this" syntax of Java in R ?) ?
Object oriented stuff in R is quite different from Java, because R 
doesn't have pointers or references except in very special cases.

Duncan Murdoch
> 
> I don't want to use a loop here.
> 
> thank you for your time and trouble,
> 
> Fran?ois.
> 
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