Hi,
It is a know issue, reported in the FAQ 7.31.
Ivan
Le 10/28/2010 13:08, Enrico R. Crema a écrit :
Well...thanks to everybody for suggestions and reading...I guess I have to
study more!
Enrico
On 28 Oct 2010, at 11:48, Rainer M Krug wrote:
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On 28/10/10 12:23, Enrico R. Crema wrote:
Dear List,
I've been running a numerical simulation and I found this odd error in my code
where the which command could not identify which rows of a column of data.frame
were corresponding to the value 0.3. There are 7 unique values in this column
(0.01,0.05,0.1,0.2,0.3,0.4,0.5), and this does not work only for 0.3. So I
looked at the column and manually tried to use the which() command, and the
results were all FALSE despite I could see those number. So I recreated my
sequence of number and tested:
seq(0.1,0.5,0.1)[3]==0.3
which gave me FALSE!!! All the other numbers (0.1,0.2,0.4,0.5) give me TRUE,
but 0.3 was not working. So I did:
seq(0.1,0.5,0.1)[3]-0.3
which gave me 5.551115e-17. If you run a similar sequence like:
seq(0.2,0.6,0.1)[2]==0.3
this will still give me FALSE. No, for my own purpose, I fixed the problem in
this way:
zerothree=seq(0.1,0.5,0.1)[3]
which(data[,1]==zerothree)
but I guess this bug is a bit of problem...Apologies if it is the wrong place
to post this bug, and apologies also if this was a known issue. My version of R
is :
platform x86_64-pc-linux-gnu
arch x86_64
os linux-gnu
system x86_64, linux-gnu
status
major 2
minor 10.1
year 2009
month 12
day 14
svn rev 50720
language R
version.string R version 2.10.1 (2009-12-14)
This is not a bug, but based on the internal representation of numbers
in the binary format. Numbers like 0.3 can not be represented as exactly
0.3, wherefore errors accumulate in a sequence.
I can't provide you a link for more details, but the topic comes up
every now and then in this mailing list.
Cheers,
Rainer
Many Thanks,
Enrico
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Rainer M. Krug, PhD (Conservation Ecology, SUN), MSc (Conservation
Biology, UCT), Dipl. Phys. (Germany)
Centre of Excellence for Invasion Biology
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______________________________________________
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PLEASE do read the posting guide http://www.R-project.org/posting-guide.html
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--
Ivan CALANDRA
PhD Student
University of Hamburg
Biozentrum Grindel und Zoologisches Museum
Abt. Säugetiere
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**********
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