[R] Help understanding environments

[Duncan Murdoch]

On 13-06-17 5:02 PM, Davis, Brian wrote:
> I have a collection of .RData files that have result objects that I would like to combine.  Specifically, skatCohort objects from the skatMeta package, but I've run into a similar issue with simple data.frames also.
>
> If I run something like
>
> FILES <- list.files(path="/path/to/my/results", pattern=".RData$", full.names=TRUE)
> combined <- NULL
>    for (FILE in FILES) {
>      load(FILE)
>      if (!is.null(combined)) {
>        combined <- c(combined, res)
>      } else {
>        combined <- res
>      }
>    }
>
> I get all my objects combined.  However, if I wrap this into a function I get the following error
>
> c_objects <- function(FILES) {
>    combined <- NULL
>    for (FILE in FILES) {
>      load(FILE)
>      if (!is.null(combined)) {
>        combined <- c(combined, res)
>      } else {
>        combined <- res
>      }
>    }
>    return(combined)
> }
>
> combined_results <- c_objects(FILES)
> Error in eval(expr, envir, enclos) : object 'combined' not found
>
> How should I write this function such that it can find "combined".   I've tried reading the help on envirnaments, and the exisits function but I haven't been able to figure this out.  Are there any other resources to read up on this?

You are doing something that you aren't showing us:  I don't see any 
calls to eval(), but it's eval() that generated the error.

Calling traceback() after the error might be informative.

Duncan Murdoch