[R] Writing a workable function

[Charles RAUX]

Since I have large data bases I only try to write a little function 
that gives the current time, reads a data frame (and assigns it) and 
at end gives the time. I have tried many forms but no one works.
Le 14 Aug 00 à 21:53, Robert Gentleman écrivait:

> Date:          Mon, 14 Aug 2000 21:53:37 +1200
> From:          Robert Gentleman <rgentlem at stat.auckland.ac.nz>
> To:            Charles RAUX <Charles.Raux at let.ish-lyon.cnrs.fr>
> Subject:       Re: [R] Writing a workable function

> On Mon, Aug 14, 2000 at 11:25:35AM +0100, Charles RAUX wrote:
> > After searching in R- Introduction, FAQ, help... I don't understand 
> > this:
> > I write a function in a file (.R):
> > tt <- function(mc) { date()
> > mc<-read.csv2("machines.txt",na.strings="")
> > date()
> > }
> > 
> > I source it in R and I type tt(). The answer is
> > > tt()
> > [1] "Mon Aug 14 11:18:25 2000"
> > >
> > The instructions following the first "date()" are ignored. Why?
>   
>   Actually they aren't. But perhaps your problem is that you don't
>  realize that in R (as in many other languages, but certainly not all)
>  parameters are passed by value. Thus, this is no way to assign a value
>  to mc.
> 
>  tt<-function() read.csv2("machines.txt",na.strings="")
>  mc<-tt()
> 
>  does what you seem to want.
>  
>  Notice that the value printed out, 
>   [1] "Mon Aug 14 11:18:25 2000"
>  is, in some sense, not the result of a call to date, both of those
>  are invisible at top level. Rather, the last call to date returns
>  that string as its value and it is that value that is returned by
>  the function and subsequently printed.
> > ---------------
> > Charles RAUX,
> > Laboratoire d'Economie des Transports
> > CNRS-Université Lumière Lyon 2-ENTPE
> > email : charles.raux at let.ish-lyon.cnrs.fr
> > http://www.ish-lyon.cnrs.fr/let
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