..............................................<°}))><........ ) ) ) ) ) ( ( ( ( ( Prof. Philippe Grosjean ) ) ) ) ) ( ( ( ( ( Numerical Ecology of Aquatic Systems ) ) ) ) ) Mons University, Belgium ( ( ( ( ( ..............................................................
On 11 Sep 2014, at 17:18, Duncan Murdoch <murdoch.dun...@gmail.com> wrote: > On 11/09/2014 3:29 AM, Philippe GROSJEAN wrote: >> On 11 Sep 2014, at 08:24, PIKAL Petr <petr.pi...@precheza.cz> wrote: >> >> > Hi >> > >> > You still do not disclose important info about details of your functions. >> > However, when you want to perform indexing like you show, you maybe can >> > get rid of NULL and use zero instead. >> > >> >> a<-1:5 >> >> a[-c(1,3)] >> > [1] 2 4 5 >> >> a[-c(0,1,3)] >> > [1] 2 4 5 >> >> a[-c(1,0,3)] >> > [1] 2 4 5 >> >> a[-c(0,1,0,3,0)] >> > [1] 2 4 5 >> > >> > However I am almost sure that you are fishing in murky waters and what you >> > do by cycle and fiddling with NULL elements can be achieved by more >> > efficiently. >> > >> … and also look at this weird case: >> >> > a <- 1:5 >> > a[-0] >> integer(0) >> > a[-c(0, 0)] >> integer(0) > > What do you find to be weird about this? As far as I can see it is acting > exactly as the documentation suggests it should: -0 is treated the same as > 0. Zero as an index selects nothing. Two zeroes also select nothing. > What's the surprise? > > Duncan Murdoch > No, it is not a surprise, nor a problem with the behaviour of R, really. It is just in connection with Petr's suggestion to replace NULL by 0. I just wanted to indicate that it could produce unwanted results in several cases. Philippe >> >> Best, >> >> Philippe >> >> >> > Regards >> > Petr >> > >> > >> >> -----Original Message----- >> >> From: r-help-boun...@r-project.org [mailto:r-help-bounces@r- >> >> project.org] On Behalf Of PO SU >> >> Sent: Thursday, September 11, 2014 3:54 AM >> >> To: Duncan Murdoch >> >> Cc: R. Help >> >> Subject: Re: [R] some question about vector[-NULL] >> >> >> >> >> >> Tks, i think using logical index is a way, but to do that, i have to >> >> keep a vector as long as the original vector. that's, to exclude >> >> position 1 and 3 from >> >> a<-1:5 >> >> I have to let b<-c(F,T,F,T,T) and exec a[b], not a[-c(1,3)]. which >> >> c(1,3) is much shorter than b if a is a long vector. that's, b would >> >> be c(F,T,F,T,T,T,T,......,T) I thought a way , >> >> let d<-c(a,1) >> >> that d<-c(1,2,3,4,5,1) >> >> and initialize the index vector iv to length(d). that is iv<-6. >> >> then, d[-iv] is always equal a[- i ] , whether i is NULL or not. >> >> Because if i is NULL ,then iv is 6, if i is 2.then iv is c(2,6) and so >> >> on....... >> >> >> >> >> >> >> >> >> >> >> >> >> >> >> >> -- >> >> >> >> PO SU >> >> mail: desolato...@163.com >> >> Majored in Statistics from SJTU >> >> >> >> >> >> >> >> >> >> At 2014-09-11 01:58:46, "Duncan Murdoch" <murdoch.dun...@gmail.com> >> >> wrote: >> >>> On 10/09/2014 12:20 PM, William Dunlap wrote: >> >>>> Can you make your example a bit more concrete? E.g., is your 'index >> >>>> vector' A an integer vector? If so, integer(0), an integer vector >> >>>> with no elements, would be a more reasonable return value than NULL, >> >>>> an object of class NULL with length 0, for the 'not found' case and >> >>>> you could check for that case by asking if length(A)==0. >> >>>> >> >>>> Show us typical inputs and expected outputs for your function (i.e., >> >>>> the problem you want to solve). >> >>> >> >>> I think the problem with integer(0) and NULL is the same: a[-i] >> >> doesn't >> >>> act as expected (leaving out all the elements of i, i.e. nothing) if i >> >>> is either of those. The solution is to use logical indexing, not >> >>> negative numerical indexing. >> >>> >> >>> Duncan Murdoch >> >>>> >> >>>> Bill Dunlap >> >>>> TIBCO Software >> >>>> wdunlap tibco.com >> >>>> >> >>>> >> >>>> On Wed, Sep 10, 2014 at 8:53 AM, PO SU <rhelpmaill...@163.com> >> >> wrote: >> >>>>> >> >>>>> Tks for your >> >>>>> >> >>>>> a <- list(ress = 1, res = NULL) >> >>>>> And in my second question, let me explain it : >> >>>>> Actually i have two vectors in global enviroment, called A and B >> >> .A is initialized to NULL which used to record some index in B. >> >>>>> Then i would run a function F, and each time, i would get a index >> >> value or NULL. that's, D<-F(B). D would be NULL or some index >> >> position in B. >> >>>>> But in the function F, though input is B, i would exclude the >> >> index value from B recorded in A. That's : >> >>>>> F<-function( B ) { >> >>>>> B<-B[-A] >> >>>>> some processing... >> >>>>> res<-NULL or some new index not included in A >> >>>>> return(res) >> >>>>> } >> >>>>> so in a loop, >> >>>>> A<-NULL >> >>>>> for( i in 1:100000) { >> >>>>> D<-F(B) >> >>>>> A<-c(A,D) >> >>>>> } >> >>>>> I never know whether D is a NULL or a different index compared >> >> with indexes already recorded in A. >> >>>>> Actually, A<-c(A,D) work well, i never worry about whether D is >> >> NULL or a real index, but in the function F, B<-B[-A] won't work. >> >>>>> so i hope that, e.g. >> >>>>> a<-1:3 >> >>>>> a[-NULL] wouldn't trigger an error but return a. >> >>>>> Because, if i wrote function like the following: >> >>>>> >> >>>>> F<-function( B ) { >> >>>>> if( is.null(A)) >> >>>>> B<-B >> >>>>> else >> >>>>> B<-B[-A] >> >>>>> some processing... >> >>>>> res<-NULL or some new index not included in A >> >>>>> return(res) >> >>>>> } >> >>>>> May be after 5 or 10 loops, A would already not NULL, so the added >> >> if ..else statement would be repeated in left 9999 loops which i would >> >> not like to see. >> >>>>> >> >>>>> >> >>>>> >> >>>>> >> >>>>> >> >>>>> -- >> >>>>> >> >>>>> PO SU >> >>>>> mail: desolato...@163.com >> >>>>> Majored in Statistics from SJTU >> >>>>> >> >>>>> >> >>>>> >> >>>>> At 2014-09-10 06:45:59, "Duncan Murdoch" >> >> <murdoch.dun...@gmail.com> wrote: >> >>>>>> On 10/09/2014, 3:21 AM, PO SU wrote: >> >>>>>>> >> >>>>>>> Dear expeRts, >> >>>>>>> I have some programming questions about NULL in R.There >> >> are listed as follows: >> >>>>>>> 1. I find i can't let a list have a element NULL: >> >>>>>>> a<-list() >> >>>>>>> a$ress<-1 >> >>>>>>> a$res<-NULL >> >>>>>>> a >> >>>>>>> str(a) >> >>>>>> >> >>>>>> You can do it using >> >>>>>> >> >>>>>> a <- list(ress = 1, res = NULL) >> >>>>>> >> >>>>>>> How can i know i have a named element but it is NULL, not just >> >> get a$xxxx,a$iiii,a$oooo there all get NULL >> >>>>>> >> >>>>>> That's a little harder. There are a few ways: >> >>>>>> >> >>>>>> "res" %in% names(a) & is.null(a[["res"]]) >> >>>>>> >> >>>>>> or >> >>>>>> >> >>>>>> identical(a["res"], list(res = NULL)) >> >>>>>> >> >>>>>> or >> >>>>>> >> >>>>>> is.null(a[[2]]) >> >>>>>> >> >>>>>> should all work. >> >>>>>> >> >>>>>> Generally because of the special handling needed, it's a bad idea >> >> to try >> >>>>>> to store NULL in a list. >> >>>>>> >> >>>>>>> 2.The most important thing: >> >>>>>>> a<-1:10 >> >>>>>>> b<-NULL or 1 >> >>>>>>> a<-c(a,b) will work so i don't need to know whether b is null or >> >> not,but: >> >>>>>>> a[-NULL] can't work!! i just need a[-NULL]==a , how can i reach >> >> this purpose? >> >>>>>> >> >>>>>> Using !, and a logical test, e.g. >> >>>>>> >> >>>>>> a[!nullentry(a)] >> >>>>>> >> >>>>>> where nullentry() is a function based on one of the tests above, >> >> but >> >>>>>> applied to all entries. >> >>>>>> >> >>>>>> Duncan Murdoch >> >>>>>> >> >>>>> ______________________________________________ >> >>>>> 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. >> >>> >> >> ______________________________________________ >> >> 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. >> > >> > ________________________________ >> > Tento e-mail a jakékoliv k němu připojené dokumenty jsou důvěrné a jsou >> > určeny pouze jeho adresátům. >> > Jestliže jste obdržel(a) tento e-mail omylem, informujte laskavě >> > neprodleně jeho odesílatele. 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Delete the contents of this e-mail with all attachments and its >> > copies from your system. >> > If you are not the intended recipient of this e-mail, you are not >> > authorized to use, disseminate, copy or disclose this e-mail in any manner. >> > The sender of this e-mail shall not be liable for any possible damage >> > caused by modifications of the e-mail or by delay with transfer of the >> > email. >> > >> > In case that this e-mail forms part of business dealings: >> > - the sender reserves the right to end negotiations about entering into a >> > contract in any time, for any reason, and without stating any reasoning. >> > - if the e-mail contains an offer, the recipient is entitled to >> > immediately accept such offer; The sender of this e-mail (offer) excludes >> > any acceptance of the offer on the part of the recipient containing any >> > amendment or variation. >> > - the sender insists on that the respective contract is concluded only >> > upon an express mutual agreement on all its aspects. >> > - the sender of this e-mail informs that he/she is not authorized to enter >> > into any contracts on behalf of the company except for cases in which >> > he/she is expressly authorized to do so in writing, and such authorization >> > or power of attorney is submitted to the recipient or the person >> > represented by the recipient, or the existence of such authorization is >> > known to the recipient of the person represented by the recipient. >> > ______________________________________________ >> > 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. >> >> ______________________________________________ >> 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. > ______________________________________________ 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.
