[R] Assign factor and levels inside function

[Tim Howard]

Andy, 
  Thank you for the help. Yes, my question really did seem like I was
going through a lot of unnecessary steps just to define levels of a
variable. But that was just for the example. In my application, I bring
new datasets into R on a daily basis. While the data differs, the
variables are the same, and the categorical variables have the same
levels. So I find myself daily applying the same factor and level
definitions (by cutting and pasting the large chunk of commands from a
text file). It really would be simpler to have it wrapped up in a
function.  That's why I asked the question about putting this into a
function.
  Upon reading your answer, I thought maybe I could use your example
and use the super-assignment '<<-' in the function. But, your method
assigns levels, but does not define the var as a factor (interesting!).

>  levels(y$one) <- seq(1, 9, by=2)
> y$one
[1] 1 1 3 3 5 7
attr(,"levels")
[1] 1 3 5 7 9
> is.factor(y$one)
[1] FALSE
> 

Unfortunately, whenever I try to use <<- with the dataframe as the
variable, I get an error message: 

> fncFact <- function(datfra){
+ datfra$one <<- factor(datfra$one, levels=c(1,3,5,7,9))
+ }
> fncFact(y)
Error in fncFact(y) : Object "datfra" not found
> 


Tim

>>> "Liaw, Andy" <andy_liaw at merck.com> 4/20/2005 4:03:24 PM >>>
Wouldn't it be easier to do this?

> levels(y$one) <- seq(1, 9, by=2)
> y$one
[1] 1 1 3 3 5 7
attr(,"levels")
[1] 1 3 5 7 9

Andy

> From: Tim Howard
> 
> R-help,
>   After cogitating for a while, I finally figured out how to define
a
> data.frame column as factor and assign the levels within a
function...
> BUT I still need to pass the data.frame and its name 
> separately. I can't
> seem to find any other way to pass the name of the data.frame,
rather
> than the data.frame itself.  Any suggestions on how to go 
> about it?  Is
> there something like value(object) or name(object) that I can't
find?
> 
> #sample dataframe for this example
> y <- data.frame(
>  one=c(1,1,3,3,5,7),
>  two=c(2,2,6,6,8,8))
> 
> > levels(y$one)   # check out levels
> NULL
> 
> # the function I've come up with
> fncFact <- function(datfra, datfraNm){
> datfra$one <- factor(datfra$one, levels=c(1,3,5,7,9))
> assign(datfraNm, datfra, pos=1)
> }
> 
> >fncFact(y, "y")
> > levels(y$one)
> [1] "1" "3" "5" "7" "9"
> 
> I suppose only for aesthetics and simplicity, I'd like to have only
> pass the data.frame and get the same result.
> Thanks in advance,
> Tim Howard
> 
> 
> > version
>          _              
> platform i386-pc-mingw32
> arch     i386           
> os       mingw32        
> system   i386, mingw32  
> status                  
> major    2              
> minor    0.1            
> year     2004           
> month    11             
> day      15             
> language R
> 
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