On 04/08/2011 11:11 AM, Doug Elias wrote:
Greetings, all ...
I'm trying to find documentation on the use of the "local()" function, and
am drawing a complete blank; would someone please send me a pointer to where
I can learn what it is intended for, and how to correctly use it?
Hi Doug --
?local
It can be useful as a function-ette giving local scope w/out cluttering
the name space or creating variables that persist after they are needed,
e.g.,
bar <- local({
txt = readLines(<some/big/file>)
## do some things to reduce big txt, e.g., sample lines
txt[sample(length(txt), 100)]
})
'bar' is now 100 lines from <some/big/file>; txt no longer exists.
It can also provide a closure, as in the 'snow' package top-level source
getMPIcluster <- NULL
setMPIcluster <- NULL
local({
cl <- NULL
getMPIcluster <<- function() cl
setMPIcluster <<- function(new) cl <<- new
})
now both getMPIcluster and setMPIcluster have access to the same
variable 'cl'; 'cl' continues to exist after the end of local() because
there are still references to it (through the environments associated
with get/set MPIcluster). This is an interesting piece of code for
understanding R's scoping, environments, and garbage collection.
Martin
Many thanks!
Doug
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