Thanks Sarah, Yes, the function behaves Exactly as documented:
check this out: > a = c(1,2,3,4,5) > a[which(a!=6)] [1] 1 2 3 4 5 > a[!which(a==6)] numeric(0) > a[-which(a==6)] numeric(0) > a[!a==6] [1] 1 2 3 4 5 I guess this is just a "gotcha", since I often use !which and -which to remove elements, So one should use a[which(a!=stuff to remove)] instead of a[-which(a==stuff to remove)] a[!which(a==stuff to remove)] Thanks, R On Sun, Feb 13, 2011 at 12:37 PM, Sarah Goslee <sarah.gos...@gmail.com> wrote: > If by "bug" you mean "function behaving exactly as documented." > > which() returns only the matches, the TRUE values. If there are no > matches, it doesn't return anything. > > If I understand what you are trying to do, and I may not, > a[which(a != 5)] > is really what you want, and it is precisely to preserve > that behavior that which() does what it does. > > Sarah > > --- > > which package:base R Documentation > > Description: > > Give the ‘TRUE’ indices of a logical object, allowing for array > indices. > > Value: > > If ‘arr.ind == FALSE’ (the default), an integer vector with > ‘length’ equal to ‘sum(x)’, i.e., to the number of ‘TRUE’s in ‘x’; > Basically, the result is ‘(1:length(x))[x]’. > > --- > On Sun, Feb 13, 2011 at 11:59 AM, Rumen Kostadinov <rkost...@gmail.com> wrote: >> Dear all, >> >> I found a bug in the which() function. >> >> When trying to remove elements with the which function, >> if the criteria is not matched, numeric(0) is returned instead of the >> array itself. >> >> This is very weird. >> >>> a = c(1,2,3,4,5) >>> a[!a==6] >> [1] 1 2 3 4 5 >>> a[-which(a==6)] >> numeric(0) >>> a[-which(a==5)] >> [1] 1 2 3 4 >>> a[!a==5] >> [1] 1 2 3 4 >> >> Is this correct? I believe this is a bug. >> >> I have to rewrite a lot of my R code to use >> a = a[!criteria] >> and not >> a = a[-which(criteria)] >> >> R. >> > > > -- > Sarah Goslee > http://www.functionaldiversity.org > ______________________________________________ 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.
