======= 2005-12-07 04:17:03 您在来信中写道:=======
>From: [EMAIL PROTECTED] >> >> ronggui a �crit : >> >> > 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 >> >> x is an argument local to mean(), >> did you expect another answer ? >> >> >>mean(x<-1:10) >> > [1] 5.5 >> >>x >> > [1] 1 2 3 4 5 6 7 8 9 10 >> >> What is the goal of this "example" ? > >I believe it's to show why "<-" is to be preferred over "=" for >assignment... Yeah,I want to show "<-" is to be preferred. Sorry for not making it clearly. >> Here with "<-", >> (voluntary, or not, side effect) >> the global variable x is, also, created. >> Did the writer really want that ??? > >Very much so, I believe. > >> I though there were other specific statements >> especially intended for global assignment, eg "<<-". > >You need to distinguish assignment in function _call_ and assignment in >function _definition_. They ain't the same. > >> If this example was intended to prove "<-" >> is better than "=" >> ... I'm not really convinced ! > >In that case, let's try another one (which is one big reason I stopped using >"=" for assignment): > > >> long.comp <- function(n) { >+ Sys.sleep(n) >+ n >+ } >> result = long.comp(30) >> system.time(result = long.comp(30)) >Error in system.time(result = long.comp(30)) : > unused argument(s) (result ...) >> system.time(result <- long.comp(30)) >[1] 0.00 0.00 30.05 NA NA >> str(result) > num 30 > >Cheers, >Andy > >> > >______________________________________________ >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 = = = = = = = = = = = = = = = = = = = = 2005-12-07 ------ Deparment of Sociology Fudan University My new mail addres is [EMAIL PROTECTED] Blog:http://sociology.yculblog.com
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