[R] Function to modify existing data.frame--Improving R Language

[Thomas Lumley]

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