Help understanding environments

-----Original Message-----
From: r-help-bounces at r-project.org [mailto:r-help-bounces at r-project.org] On Behalf
Of Rui Barradas
Sent: Tuesday, June 18, 2013 7:57 AM
To: Davis, Brian
Cc: r-help at r-project.org
Subject: Re: [R] Help understanding environments

Hello,

The first argument to exists() must be the name of an object given as a
character string, as stated in the help page. See ?exists. You have also
forgot to initialize combined to NULL, this time.
Your function revised would then become


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


And all works as expected.

Hope this helps,

Rui Barradas


Em 18-06-2013 14:57, Davis, Brian escreveu:

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