R help - Feb 2005 - Programming/scripting with "expressions - variables"

Hello to Rusers!

I am puzzled with R and I really do not know where to look
in for my problem. I am moving from SAS and I have difficulties
in translating SAS to R world. I hope I will get some hints 
or pointers so I can study from there on.

I would like to do something like this. In SAS I can write 
a macro as example bellow, which is afcourse a silly one but 
shows what I don't know how to do in R.

%macro test(data, colname, colvalue);
    data &data;
        ...
        &colname="&colvalue";
        other_&colname="other_&colvalue";
    run;
%mend;

And if I run it with this call:
%test(Gregor, Gorjanc, 25);

I get a table with name 'Gregor' and columns 'Gorjanc', 
and 'other_Gorjanc' with values:

Gorjanc other_Gorjanc
"25"    "other_25"

So can one show me the way to do the same thing in R? 

Thanks!

--
Lep pozdrav / With regards,
    Gregor GORJANC

---------------------------------------------------------------
University of Ljubljana
Biotechnical Faculty       URI: http://www.bfro.uni-lj.si
Zootechnical Department    email: gregor.gorjanc <at> bfro.uni-lj.si
Groblje 3                  tel: +386 (0)1 72 17 861
SI-1230 Domzale            fax: +386 (0)1 72 17 888
Slovenia

Here is one way.  It is the custom to return a value that will be assigned
to the variable, so I changed your 'macro' to a function that returns
the
value and then assigns it to your variable:
> test <- function(name, value){
+     .result <- NULL # initialize to NULL
+     .result[name] <- value
+     .result[paste('other_', name, sep='')] <-
paste("other_", value,
sep='')
+     .result
+ }
> Gregor <- test('Gorjanc', '25')
> Gregor    # print out the vector
      Gorjanc other_Gorjanc
         "25"    "other_25"
>
__________________________________________________________
James Holtman        "What is the problem you are trying to solve?"
Executive Technical Consultant  --  Office of Technology, Convergys
james.holtman at convergys.com
+1 (513) 723-2929



                      "Gorjanc Gregor"
                      <Gregor.Gorjanc at bfro.        To:       <r-help at
stat.math.ethz.ch>
                      uni-lj.si>                   cc:
                      Sent by:                     Subject:  [R]
Programming/scripting  with "expressions - variables"
                      r-help-bounces at stat.m
                      ath.ethz.ch


                      02/07/2005 09:52






Hello to Rusers!

I am puzzled with R and I really do not know where to look
in for my problem. I am moving from SAS and I have difficulties
in translating SAS to R world. I hope I will get some hints
or pointers so I can study from there on.

I would like to do something like this. In SAS I can write
a macro as example bellow, which is afcourse a silly one but
shows what I don't know how to do in R.

%macro test(data, colname, colvalue);
    data &data;
        ...
        &colname="&colvalue";
        other_&colname="other_&colvalue";
    run;
%mend;

And if I run it with this call:
%test(Gregor, Gorjanc, 25);

I get a table with name 'Gregor' and columns 'Gorjanc',
and 'other_Gorjanc' with values:

Gorjanc other_Gorjanc
"25"    "other_25"

So can one show me the way to do the same thing in R?

Thanks!

--
Lep pozdrav / With regards,
    Gregor GORJANC

---------------------------------------------------------------
University of Ljubljana
Biotechnical Faculty       URI: http://www.bfro.uni-lj.si
Zootechnical Department    email: gregor.gorjanc <at> bfro.uni-lj.si
Groblje 3                  tel: +386 (0)1 72 17 861
SI-1230 Domzale            fax: +386 (0)1 72 17 888
Slovenia

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Gorjanc Gregor wrote:
> Hello to Rusers!
> 
> I am puzzled with R and I really do not know where to look
> in for my problem. I am moving from SAS and I have difficulties
> in translating SAS to R world. I hope I will get some hints 
> or pointers so I can study from there on.
> 
> I would like to do something like this. In SAS I can write 
> a macro as example bellow, which is afcourse a silly one but 
> shows what I don't know how to do in R.
> 
> %macro test(data, colname, colvalue);
>     data &data;
>         ...
>         &colname="&colvalue";
>         other_&colname="other_&colvalue";
>     run;
> %mend;
> 
> And if I run it with this call:
> %test(Gregor, Gorjanc, 25);
> 
> I get a table with name 'Gregor' and columns 'Gorjanc', 
> and 'other_Gorjanc' with values:
> 
> Gorjanc other_Gorjanc
> "25"    "other_25"
> 
> So can one show me the way to do the same thing in R? 
> 
> Thanks!
> 
> --
> Lep pozdrav / With regards,
>     Gregor GORJANC
> 
Greetings, Gregor, from a fan of Slovenia.

Here is a start.  Multiple variables are often put together in data 
frames.  Your example did not include an input dataset name.  I took 
data to be an input data frame, and added two new variables.  I assume 
that colvalue and colname are character values.  If colvalue has length 
one it will be duplicated for each row of data.

test <- function(data, colname, colvalue) {
   data[[colname]] <- colvalue
   data[[paste('other',colname,sep='_')]] <-
paste('other',colvalue,sep='_')
   data
}

Example usage:

data <- data.frame(x=1:5, y=11:15)
data2 <- test(data, 'a', 'b')
data <- test(data, 'a', 'b')  # over-write
test(data, 'a', 'b')          # create data but don't store
with(test(data, ....),{...})        # reference variables in temporary 
dataset

If we know what your ultimate goal is, there may be a much better 
approach than the test function.  In many cases, you do not need to 
create new variables at all.

Franc
-- 
Frank E Harrell Jr   Professor and Chair           School of Medicine
                      Department of Biostatistics   Vanderbilt University