[R] Bug in rep() function
Prof Brian Ripley
ripley at stats.ox.ac.uk
Mon Sep 15 18:36:42 CEST 2014
On 15/09/2014 16:30, Samuel Knapp wrote:
> Dear all,
>
> I have discovered a bug in the standard rep() function: At certain
Not 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
>
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--
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
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