R help - Jan 2005 - Function to modify existing data.frame--Improving R Language

Thanks to everyone who replied to my question!

A comment regarding Thomas's point below:  Java & other object-oriented
languages that are function rather than macro based usually provide methods
& other capabilities that allow pass by reference in certain cases and these
methods would solve the problem I posed regarding how to change values in an
existing data.frame from within a function.  In Java, for example, objects
pass by reference, so I could easily transfer a dataset to a function & have
it efficiently changed.  In Visual Basic, one could indicate whether a
variable was being passed by reference or value.  By not allowing any
straightforward passing by reference, R strikes me as a lot less flexible &
useful than it might be.  A basic operation in other stats languages is to
update a dataset using a program.  This proves very helpful for managing
data and setting up analyses.  But, this seems to be quite inelegant to do
in R.

Peter

On 1/19/05 6:16 AM, "r-help-request at stat.math.ethz.ch" From: Thomas
Lumley
<tlumley at u.washington.edu>
<r-help-request at stat.math.ethz.ch> wrote:
> Yes and no.
> 
> This isn't so much a question of pass-by-reference, as one reply
> suggested, but of macros vs functions.
> 
> Stata is (largely) a macro language: it does operations on command strings
> and then evaluates them.  It's not that Stata programs work with
> references, it's that all objects (except local macros) are global.
> 
> R is based on functions: it evaluates arguments and then operates on
> them.  When you have functions, with local variables, it then becomes
> relevant to ask whether the arguments to the function are just copies or
> are references to the real thing. In R they are just copies (from a
> language point of view) but are often references from an efficiency point
> of view.

On Wed, 19 Jan 2005, Peter Muhlberger wrote:
> 						 By not allowing any
> straightforward passing by reference, R strikes me as a lot less flexible
&
> useful than it might be.  A basic operation in other stats languages is to
> update a dataset using a program.  This proves very helpful for managing
> data and setting up analyses.  But, this seems to be quite inelegant to do
> in R.
I don't see why
     mydata <- some.program(mydata)
is much less elegant than
     mydata.someProgram()
as a way of updating a data set. It may use more memory, but that wasn't 
the point at issue.

Of course there are advantages to the ability to pass by reference, and 
disadvantages -- the most obvious disadvantage is that it is not easy to 
tell which variables are modified by a given piece of code.

It probably wouldn't be that hard to produce something that looked like a 
data frame but was passed by reference, by wrapping it in a environment.

 	-thomas



>
> Peter
>
> On 1/19/05 6:16 AM, "r-help-request at stat.math.ethz.ch" From:
Thomas Lumley
> <tlumley at u.washington.edu>
> <r-help-request at stat.math.ethz.ch> wrote:
>
>> Yes and no.
>>
>> This isn't so much a question of pass-by-reference, as one reply
>> suggested, but of macros vs functions.
>>
>> Stata is (largely) a macro language: it does operations on command
strings
>> and then evaluates them.  It's not that Stata programs work with
>> references, it's that all objects (except local macros) are global.
>>
>> R is based on functions: it evaluates arguments and then operates on
>> them.  When you have functions, with local variables, it then becomes
>> relevant to ask whether the arguments to the function are just copies
or
>> are references to the real thing. In R they are just copies (from a
>> language point of view) but are often references from an efficiency
point
>> of view.
>
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Thomas Lumley			Assoc. Professor, Biostatistics
tlumley at u.washington.edu	University of Washington, Seattle