[R] Extracting an object name?

[Duncan Murdoch]

On 24/04/2009 9:30 PM, greggallen at gmail.com wrote:
> Dear Sir or Madam:
> 
> This is an extension to a earlier post, about looping through several
> thousand files, and testing student's models against a different
> data-set, called rclnow, for "recall now".
> 
> The problem is, that the instructor never specified to the students,
> what they should name their "lm" object.
> 
> So what they created was:
> "arbitrary variable name" <- lm(Y~(V1+V2+.... more stuff), learn_data_frame)
> 
> Now there are 1500+ files that are named:
> "BIOtotals_students_name_class_name_date_other_info..."
> "BIOtotals_more_stuff_2.."
> "BIOtotal_more-stuff_3
> ......................
> ......................
> 
> 
> Now I always get this error in the "predict" statement:
> 
> Error in UseMethod("predict") : no applicable method for "predict"
> 
> Is there a way to pass the unknown object name to predict, or do we
> need to ask the students to redo all the work with a given model name?
> (I hope not!)

predict() doesn't want an object name, it wants an object.  load() 
returns an object name, and loads the object.  So you can find the 
object by the name that gets loaded.

If the students only created one object, you could do it as

name <- load(s)
model <- get(name)

but that's dangerous:  if you don't know what the student named the 
model, then you don't want to load it in with all your other variables. 
  So a safer way to go is:

studentvars <- new.env()
names <- load(s, studentvars)

Now figure out which of the names is the model (say names[1]), and do
model <- get(names[1], envir=studentvars)

Duncan Murdoch

> 
> function(L)
> {
> fname <- format(Sys.time(), 'Totals_%b%d_%H%M_%S.txt')
> filesused <- format(Sys.time(), 'Files_%b%d_%H%M_%S.txt')
> setwd("/Users/gregg/R_system")
> dire <- getwd()
> print(dire)
> flies <- list.files(pattern = "BIOtotal*")# flies instead of files
> because of FEAR of reserved words!!!
> for(i in 1:length(flies))
> {
> s <-   flies[i]
> print(i) # print everything for debugging
> print(s)
> model <- load(s)
> print(model)
> z  <- predict( model ,rclnow) ##############  what will model be?????
> print(z)
> write( z, fname   , append = TRUE,  ncolumns = L)
> write( as.character(s) , filesused   , append = TRUE,  ncolumns = 1 )
> }
> }
> 
> 
> THANKS for any help!
> 
> Greg Allen
> 
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