[R] 0.3 is not 0.3, bug in seq() function?

[Rubén Roa]

Enrico,

The same happens with other numbers/sequences.
seq(0.1,0.9,0.1)[7]==0.7
[1] FALSE
seq(0.1,1.3,0.1)[12]==1.2
[1] FALSE

Rounding seems to fix it,

round(seq(0.1,0.5,0.1),1)[3]==0.3
round(seq(0.1,0.9,0.1),1)[7]==0.7
round(seq(0.1,1.3,0.1),1)[12]==1.2

They all return TRUE.

____________________________________________________________________________________ 

Dr. Rubén Roa-Ureta
AZTI - Tecnalia / Marine Research Unit
Txatxarramendi Ugartea z/g
48395 Sukarrieta (Bizkaia)
SPAIN



> -----Mensaje original-----
> De: r-help-bounces at r-project.org 
> [mailto:r-help-bounces at r-project.org] En nombre de Enrico R. Crema
> Enviado el: jueves, 28 de octubre de 2010 12:24
> Para: r-help at r-project.org
> Asunto: [R] 0.3 is not 0.3, bug in seq() function?
> 
> 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)
> 
> 
> Many Thanks,
> 
> Enrico
> 
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