From: Berwin A Turlach <berwin_at_maths.uwa.edu.au>

Date: Wed 07 Dec 2005 - 12:57:26 EST

>> [1] 5.5

>>> x

>> Error: object "x" not found

>> [1] 5.5

>>> x

>> [1] 1 2 3 4 5 6 7 8 9 10

R-help@stat.math.ethz.ch mailing list

https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide! http://www.R-project.org/posting-guide.html Received on Wed Dec 07 13:05:05 2005

Date: Wed 07 Dec 2005 - 12:57:26 EST

>>>>> "vic" == vincent <vincent@7d4.com> writes:

vic> ronggui a $A(&(Bcrit :

>> I think it is NOT just for historical reason. see the

* >> following example:
** >>
*

>>> rm(x) mean(x=1:10)

>> [1] 5.5

>>> x

>> Error: object "x" not found

vic> x is an argument local to mean(), did you expect another vic> answer ?

>>> mean(x<-1:10)

>> [1] 5.5

>>> x

>> [1] 1 2 3 4 5 6 7 8 9 10

vic> What is the goal of this "example" ? I believe to demonstrate that "<-" is preferable.

vic> Here with "<-", (voluntary, or not, side effect) the global
vic> variable x is, also, created.

Who says that the variable x is global? The example above looks as if
it was typed on the command line and, hence, x would be global. But
the same piece of code could be inside a function with x being a
variable local to that function.

vic> Did the writer really want that ??? Yes. Perhaps a more realistic example is the following:

> library(MASS) > par(mfrow=c(2,2)) > plot( fm <- lm(log(brain) ~ log(body), mammals) )

A construct I use frequently to fit a linear model and obtain the diagnostic plots at the same time. And I had students appearing in my office complaining that the code in the lab sheet produced errors and swearing that they typed in exactly what I have written on the lab sheet. But, of course, they had substituted "=" for "<-"

vic> I though there were other specific statements especially vic> intended for global assignment, eg "<<-". As you say, these are for global assignments. Nobody said that in rongui's example "x" or in my example "fm" is a global variable. They could be local to a function.

Cheers,

Berwin

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Berwin A Turlach Tel.: +61 (8) 6488 3338 (secr)
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R-help@stat.math.ethz.ch mailing list

https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide! http://www.R-project.org/posting-guide.html Received on Wed Dec 07 13:05:05 2005

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