R help - May 2014 - referencing a data frame with a pointer, link, alias, etc

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, ...)

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. 



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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

Yes and no. There are "lists" that can hold anything, but for normal
objects there are no "pass by reference" semantics. The exception to
that is environments, but that is really a limited scope of usability. That is,
you can receive a changed object in the calling scope and choose to overwrite
your original variable if you choose.

If you provided the "minimal reproducible example" asked for you might
get some code examples in return.
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Go...
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Sent from my phone. Please excuse my brevity.

On May 29, 2014 1:13:10 PM PDT, dansawyer <dansawyer at earthlink.net>
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, ...)
>
>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. 
>
>
>
>--
>View this message in context:
>http://r.789695.n4.nabble.com/referencing-a-data-frame-with-a-pointer-link-alias-etc-tp4691436.html
>Sent from the R help mailing list archive at Nabble.com.
>
>______________________________________________
>R-help at r-project.org mailing list
>https://stat.ethz.ch/mailman/listinfo/r-help
>PLEASE do read the posting guide
>http://www.R-project.org/posting-guide.html
>and provide commented, minimal, self-contained, reproducible code.

On Thu, 29 May 2014 01:13:10 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, ...)
> 
> 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.
> 
> 
Hi dansawyer,
I may not completely understand what you want to do, but I think you 
want the "get" function to sequentially process your dataframes. 
Maybe something like this:

for(df in paste("df",1:10,sep="")) {
 var<-get(df)
 #do your processing on "var"
}

If you want to read in say, CSV files one at a time:

for(df in paste("df",1:10,".csv",sep="")) {
 var<-read.csv(df)
 #do your processing on "var"
}

You may also want to define a class that specifies the structure of your 
dataframes.

Jim