[R] referencing a data frame with a pointer, link, alias, etc

[David Winsemius]

On May 29, 2014, at 1:13 PM, dansawyer wrote:

> Good afternoon. 
> 
> The question is: does R support pointer like structures? The specific
> problem is:
> 
> a function supporting operations on a set of data frames with similar
> structures. 
> 
> I have a set of data frames with similar structures. I wish to perform
> similar operations on those data frames. I have successfully created and
> tested the operations and am ready to write a local function to perform
> them. To clarify the question below is a pigeon example for the question: 
> 
> df1 <- (col1, col2, ...)
> df2 <- (col1, col2, ...)

Not valid R code.

> 
> function f(var)
> {var$col1 <- ...
> var$col2 <- ...
> }
> 
> f(df1)
> 
> Each of the data frames have common column names
> 
> I would like for f to be able to perform operations on the data frames from
> within the function. I have tried testing variables without success. R
> allows for creating the necessary 'strings' with the correct names, however
> I am unable to bind, transform those strings to reference the data frames. 

Learn to use "[[" instead of "$". (There is a warning about not doing what you are doing in the help page for ?"$" .)

And furthermore when you see this message (which Nabble rather impolitely removes)
"and provide commented, minimal, self-contained, reproducible code."  ... it means real R code and not pseudo-code as you are currently offering.


David Winsemius
Alameda, CA, USA