Change your 'fileIndex <- fileIndex + 1' to 'fileIndex <<- fileIndex + 1'
so the fileIndex in the environment of the call to generateFiles() is altered
(instead of creating and forgetting about a variable called fileIndex
in the function created by generateFiles.
generateFiles <- function(path, pattern="\\.xml$") {
files <- dir(path, pattern=pattern, full.names=TRUE, recursive=TRUE,
no..=TRUE)
total <- length(files)
fileindex <- 1
fileGen <- function() {
if (fileindex < total) {
fileToReturn <- files[[fileindex]]
print(fileindex)
fileindex <<- fileindex + 1
fileToReturn
}
}
fileGen
}
used as:
> nextFile <- generateFiles("c:/temp", pattern="\\.R$")
> nextFile()
[1] 1
[1] "c:/temp/4209/test.R"
> nextFile()
[1] 2
[1] "c:/temp/a.R"
Bill Dunlap
Spotfire, TIBCO Software
wdunlap tibco.com
> -----Original Message-----
> From: r-help-boun...@r-project.org [mailto:r-help-boun...@r-project.org] On
> Behalf
> Of Ashwani Rao
> Sent: Monday, August 12, 2013 9:45 AM
> To: r-help@r-project.org
> Subject: [R] function closure
>
> Hi,
>
> Just for fun, I wanted to try function closures.
> Here is simple function definition.
> The following "generateFiles" function return function "fileGen" which will
> return a a regular file in directory , every time a call it (fileGen).
>
>
> generateFiles <- function(path, pattern="*.xml")
>
> {
>
> files <- dir(path, pattern="*.xml", full.names=TRUE, recursive=TRUE,
> no..=TRUE)
>
> total <- length(files)
>
> fileindex = 1
>
> fileGen <- function()
>
> {
>
> if (fileindex > total)
>
> {
>
> return(NULL)
>
> }
>
> fileToReturn <- files[[fileindex]]
>
> print(fileindex)
>
> fileindex <- fileindex + 1
>
> return(fileToReturn)
>
> }
>
> return(fileGen)
>
> }
>
>
> I am incrementing the value of variable "fileindex" in the function
> "fileGen" , everytime I call this function.
>
> But the value of fileindex remains 1 , no matter how many times i call
> "fileGen()".
>
> Can you please tell me how to change the value of fileIndex so as in
> subsequent call to "fileGen" will reflect this.
> --
> अश्वनी प्रताप
>
> [[alternative HTML version deleted]]
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