[R] Help understanding environments

[Davis, Brian]

In my haste to make a smaller example than my actual code I used 'is.null' instead of 'exists' as is in my code.  Here's a small reproducible example


res <- list(abc=letters, ABC=LETTERS)
save(res, file="results.RData")
res <- list(zyx=rev(letters), ZYX=rev(LETTERS))
save(res, file="results2.RData")

rm(res)
FILES <- c("results.RData", "results2.RData")


c_objects <- function(FILES) {
  for (FILE in FILES) {
    load(FILE)
    if (exists(combined)) {
      combined <- c(combined, res)
    } else {
      combined <- res
    }
  }
  return(combined)
}

combined_results <- c_objects(FILES)


-----Original Message-----
From: Duncan Murdoch [mailto:murdoch.duncan at gmail.com] 
Sent: Monday, June 17, 2013 5:40 PM
To: Davis, Brian
Cc: r-help at r-project.org
Subject: Re: [R] Help understanding environments

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