It really suprise me that a[-c(0,1,2)] works as a[-c(1,2)]. But, unfortunately, a[-0] still can't work . That 's mean: i want: a<-1:3 a[-0] > 1 2 3 or a[-NULL] > 1 2 3
-- PO SU mail: [email protected] Majored in Statistics from SJTU At 2014-09-11 02:24:25, "PIKAL Petr" <[email protected]> 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. > >Regards >Petr > > >> -----Original Message----- >> From: [email protected] [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: [email protected] >> Majored in Statistics from SJTU >> >> >> >> >> At 2014-09-11 01:58:46, "Duncan Murdoch" <[email protected]> >> 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 <[email protected]> >> 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: [email protected] >> >> > Majored in Statistics from SJTU >> >> > >> >> > >> >> > >> >> > At 2014-09-10 06:45:59, "Duncan Murdoch" >> <[email protected]> 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 >> >> >> >> >> > ______________________________________________ >> >> > [email protected] 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. >> > >> ______________________________________________ >> [email protected] 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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