[R] 'require' equivalent for local functions

[Gabor Grothendieck]

Try this:

if (!exists("myfun", mode = "function")) source("myfile.R")

Also check the other arguments of exists in case you want to
restrict the search.

On Sun, Mar 22, 2009 at 5:05 PM, JiHO <jo.lists at gmail.com> wrote:
> Hello everyone,
>
> I often create some local "libraries" of functions (.R files with only
> functions in them) that I latter call. In scripts that call a function from
> such library, I would like to be able to test whether the function is
> already known in the namespace and, only if it is not, source the library
> file. I.e. what `require` does for packages, I want to do with my local
> functions.
>
> Example:
> lib.R
>        foo <- function(x) { x*2 }
>
> script.R
>        require.local(foo,"lib.R")
>        # that searches for function "foo" and, if not found, executes
> source("lib.R")
>        foo(2)
>
> Obviously, I want the test to be quite efficient otherwise I might as well
> source the local library every time. I am aware that it would probably not
> be able to check for changes in lib.R (i.e. do complicated things such as
> re-source lib.R if foo in the namespace and foo in lib.R are different), but
> that I can handle manually.
>
> This seems like a common enough workflow but I cannot find a pre-existing
> solution. Does anyone have pointers?
>
> Otherwise I tried to put that together:
>
> require.local <- function(fun, lib)
> #
> #       Searches for function "fun" and sources "lib" in
> #       case it is not found
> #
> {
>        if (! (deparse(substitute(fun)) %in% ls(".GlobalEnv") && class(fun)
> == "function") ) {
>                cat("Sourcing", lib,"...\n")
>                source(lib)
>        }
> }
>
> but I am really not confident with all those deparse/substitute things and
> the environment manipulation, so I guess there should be a better way.
>
> JiHO
> ---
> http://jo.irisson.free.fr/
>
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