R help - Jun 2009 - altering a global variable

I'm working on a program that loads several large data files.  I'm  
using ddply (plyr is really awesome) but I want to minimize the amount  
of times a large data file is read in.  One solution is to keep track  
of which data file is open with a global variable and then change the  
currently open data file globally as needed.  However, I'm unclear on  
how to alter a global variable from within a function.  For example

m<-3
a<-function(x) m<-4

a(3)

m

shows that m is still 3 at the end of it all.  With the code above,  
how could I modify the function a to actually set m to whatever value  
I wanted globally?

Thanks for any pointers!

-Jarrett




----------------------------------------
Jarrett Byrnes
Postdoctoral Associate, Santa Barbara Coastal LTER
Marine Science Institute
University of California Santa Barbara
Santa Barbara, CA 93106-6150
http://www.lifesci.ucsb.edu/eemb/labs/cardinale/people/byrnes/index.html


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Try:


a <- function(x)m<<-4

On Mon, Jun 15, 2009 at 3:10 PM, Jarrett Byrnes <byrnes@msi.ucsb.edu>
wrote:
> I'm working on a program that loads several large data files.  I'm
> using ddply (plyr is really awesome) but I want to minimize the amount
> of times a large data file is read in.  One solution is to keep track
> of which data file is open with a global variable and then change the
> currently open data file globally as needed.  However, I'm unclear on
> how to alter a global variable from within a function.  For example
>
> m<-3
> a<-function(x) m<-4
>
> a(3)
>
> m
>
> shows that m is still 3 at the end of it all.  With the code above,
> how could I modify the function a to actually set m to whatever value
> I wanted globally?
>
> Thanks for any pointers!
>
> -Jarrett
>
>
>
>
> ----------------------------------------
> Jarrett Byrnes
> Postdoctoral Associate, Santa Barbara Coastal LTER
> Marine Science Institute
> University of California Santa Barbara
> Santa Barbara, CA 93106-6150
> http://www.lifesci.ucsb.edu/eemb/labs/cardinale/people/byrnes/index.html
>
>
>        [[alternative HTML version deleted]]
>
> ______________________________________________
> R-help@r-project.org mailing list
> https://stat.ethz.ch/mailman/listinfo/r-help
> PLEASE do read the posting guide
> http://www.R-project.org/posting-guide.html
> and provide commented, minimal, self-contained, reproducible code.
>


-- 
Henrique Dallazuanna
Curitiba-Paraná-Brasil
25° 25' 40" S 49° 16' 22" O

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