Dear all,
I have discovered a bug in the standard rep() function: At certain
values, rep() does not replicate the element by the proper number of times:
> a <- (1-0.9)*100
> a
[1] 10
> length(rep(1,times=a))
[1] 9
> length(rep(1,each=a))
[1] 9
As shown, this happens as well for the times= as for the each=
parameter. It does not depend on the kind of element that is to be repeated:
> length(rep("abc",each=a))
[1] 9
I tried to narrow down the bug, but haven't really managed to find a
pattern behind the bug. Here is a list with values for a (see above)
that returns a false object ( after the value for a, i've collected the
expected length and the length that is produced by r):
# mistake at
(1-0.9)*100 10 9
(1-0.8)*100 20 19
(1-0.8)*1000 200 199
(1-0.9)*1000 100 99
(1-0.9)*10 1 0
(1-0.8)*10 2 1
(1-0.9)*1000000000 100000000 99999999
(2-1-0.9)*100 10 9
(10/10-0.9)*100 10 9
# the following sets for a work fine
(1+0.1)*100
(1-0.1)*100
(1-0.7)*100
(1-0.99)*1000
(1-0.7)*10
(1-0.90)*10
(1-0.95)*100
(1-0.95)*1000
(2-0.9)*1000
(2-1.9)*100
(1.1-1)*100
(10-9)*100
Did I make any mistake? Or where else should I address this problem?
Thanks and best regards,
Samuel
No, actually you've discovered FAQ 7.31.> a <- (1-0.9)*100 > a[1] 10> print(a, digits=20)[1] 9.9999999999999982236 In combination with the description in ?rep: Non-integer values of ?times? will be truncated towards zero. If ?times? is a computed quantity it is prudent to add a small fuzz. you get 9 times. The best thing to do is ensure that your values are integer *before* passing them to rep(), unless you know that truncating toward zero is the right thing to do. Sarah On Mon, Sep 15, 2014 at 11:30 AM, Samuel Knapp <samuel.k at gmx.de> wrote:> Dear all, > > I have discovered a bug in the standard rep() function: At certain values, > rep() does not replicate the element by the proper number of times: > >> a <- (1-0.9)*100 >> a > [1] 10 >> length(rep(1,times=a)) > [1] 9 >> length(rep(1,each=a)) > [1] 9 > > As shown, this happens as well for the times= as for the each= parameter. It > does not depend on the kind of element that is to be repeated: > >> length(rep("abc",each=a)) > [1] 9 > > I tried to narrow down the bug, but haven't really managed to find a pattern > behind the bug. Here is a list with values for a (see above) that returns a > false object ( after the value for a, i've collected the expected length and > the length that is produced by r): > > # mistake at > (1-0.9)*100 10 9 > (1-0.8)*100 20 19 > (1-0.8)*1000 200 199 > (1-0.9)*1000 100 99 > (1-0.9)*10 1 0 > (1-0.8)*10 2 1 > (1-0.9)*1000000000 100000000 99999999 > (2-1-0.9)*100 10 9 > (10/10-0.9)*100 10 9 > > # the following sets for a work fine > (1+0.1)*100 > (1-0.1)*100 > (1-0.7)*100 > (1-0.99)*1000 > (1-0.7)*10 > (1-0.90)*10 > (1-0.95)*100 > (1-0.95)*1000 > (2-0.9)*1000 > (2-1.9)*100 > (1.1-1)*100 > (10-9)*100 > > Did I make any mistake? Or where else should I address this problem? > > Thanks and best regards, > Samuel >-- Sarah Goslee http://www.functionaldiversity.org
On 15/09/2014 16:30, Samuel Knapp wrote:> Dear all, > > I have discovered a bug in the standard rep() function: At certainNot so: > a <- (1-0.9)*100 > trunc(a) [1] 9 As the help says Non-integer values of ?times? will be truncated towards zero. If ?times? is a computed quantity it is prudent to add a small fuzz. And as the posting guide said Do your homework before posting: ... Read the online help for relevant functions (type ?functionname, e.g., ?prod, at the R prompt)> values, rep() does not replicate the element by the proper number of times: > > > a <- (1-0.9)*100 > > a > [1] 10 > > length(rep(1,times=a)) > [1] 9 > > length(rep(1,each=a)) > [1] 9 > > As shown, this happens as well for the times= as for the each> parameter. It does not depend on the kind of element that is to be > repeated: > > > length(rep("abc",each=a)) > [1] 9 > > I tried to narrow down the bug, but haven't really managed to find a > pattern behind the bug. Here is a list with values for a (see above) > that returns a false object ( after the value for a, i've collected the > expected length and the length that is produced by r): > > # mistake at > (1-0.9)*100 10 9 > (1-0.8)*100 20 19 > (1-0.8)*1000 200 199 > (1-0.9)*1000 100 99 > (1-0.9)*10 1 0 > (1-0.8)*10 2 1 > (1-0.9)*1000000000 100000000 99999999 > (2-1-0.9)*100 10 9 > (10/10-0.9)*100 10 9 > > # the following sets for a work fine > (1+0.1)*100 > (1-0.1)*100 > (1-0.7)*100 > (1-0.99)*1000 > (1-0.7)*10 > (1-0.90)*10 > (1-0.95)*100 > (1-0.95)*1000 > (2-0.9)*1000 > (2-1.9)*100 > (1.1-1)*100 > (10-9)*100 > > Did I make any mistake? Or where else should I address this problem? > > Thanks and best regards, > Samuel > > ______________________________________________ > R-help at 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.-- Brian D. Ripley, ripley at stats.ox.ac.uk Emeritus Professor of Applied Statistics, University of Oxford 1 South Parks Road, Oxford OX1 3TG, UK