try this > 0.3-0.1 == 0.2 [1] FALSE > round(0.3-0.1,1)==round(0.2,1) [1] TRUE
liov 2009/4/21 Marc Schwartz <marc_schwa...@me.com> > On Apr 21, 2009, at 5:55 AM, Duncan Murdoch wrote: > > On 21/04/2009 3:48 AM, Petr PIKAL wrote: >> >>> Hi >>> r-help-boun...@r-project.org napsal dne 20.04.2009 19:01:46: >>> >>>> wolfgang.siewert <wolfgang.siewert <at> gmail.com> writes: >>>> >>>> There is a way around: round(0.7-0.3,1)==0.4 >>>>> (TRUE) >>>>> >>>>> Obviously there is a problem with some combinations of decimal >>>>> >>>> subtractions, >>> >>>> that - we have the feeling - shouldt be solved. >>>>> >>>> Oh no, not that one again! This was lecture two in my first computer >>>> course in 1968, but it seems to be gone the way of the dodo since than. >>>> >>> Maybe that is because of Excel is so widespread now and gives expected >>> results (it probably silently rounds all decimal numbers before >>> calculation). >>> >> >> I don't have Excel, but I expect OpenOffice duplicates its bugs pretty >> well. And in OpenOffice I see all sorts of bugs due to this, e.g. examples >> where x = y and y = z but x != z, cases where I can calculate a number like >> 1 + 4.e-15 and get something different from 1, but if I enter it directly as >> 1.000000000000004, it gets changed to 1. >> >> So it only gives expected results in some tests, not others. >> >> Duncan Murdoch >> > > > > As Dieter noted from our offlist exchange, this had been discussed > previously back in 2003. Just to refresh memories: > > https://stat.ethz.ch/pipermail/r-help/2003-June/034565.html > > https://stat.ethz.ch/pipermail/r-help/2003-June/034860.html > > > OO.org has replicated Excel's behavior to a fault. Thus: > > Spreadsheet Use -> Brain to Porridge > > > Just to update OO.org's behavior using version 3.0.1 on OSX: > > Formula: =4.145 * 100 + 0.5 Result: 415.00000000000000000000 > > Formula: =0.5 - 0.4 - 0.1 Result: 0.00000000000000000000 > > Formula: =(0.5 - 0.4 - 0.1) Result: 0.00000000000000000000 > > So nothing has changed in OO.org in five years. Somebody with Excel 2007 > might want to try the 2nd and 3rd formula examples to see if using parens > still makes a difference in the result as compared to the formula without > the parens. > > > FWIW, now that I am on OSX, I can add the following output using Numbers > '09: > > Formula: =4.145 * 100 + 0.5 Result: 415.00000000000000000000 > > Formula: =0.5 - 0.4 - 0.1 Result: -2.77556E-17 > > Formula: =(0.5 - 0.4 - 0.1) Result: -2.77556E-17 > > > It does look like R's behavior has changed since then. Using: > > R version 2.9.0 Patched (2009-04-18 r48348) > > on OSX: > > # This first example has changed. > # Prior result was 414.99999999999994 > > print(4.145 * 100 + 0.5, digits = 20) > [1] 415 > > > formatC(4.145 * 100 + 0.5, format = "E", digits = 20) > [1] "4.14999999999999943157E+02" > > > print(0.5 - 0.4 - 0.1, digits = 20) > [1] -2.77555756156289e-17 > > > formatC(0.5 - 0.4 - 0.1, format = "E", digits = 20) > [1] "-2.77555756156289135106E-17" > > > What is interesting is that: > > > 4.145 * 100 + 0.5 == 415 > [1] FALSE > > > (4.145 * 100 + 0.5) - 415 > [1] -5.684342e-14 > > > all.equal(4.145 * 100 + 0.5, 415, 0) > [1] "Mean relative difference: 1.369721e-16" > > > So it would appear that in the first R example above, the print() function > has changed in a material fashion. > > HTH, > > Marc Schwartz > > > ______________________________________________ > 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. > -- Luis Iván Ortiz Valencia Estatístico Msc. ............................................... Curriculum Lattes http://buscatextual.cnpq.br/buscatextual/visualizacv.jsp?id=K4778724J3 ............................................... http://oplanetaliov.blogspot.com/ ............................................... [[alternative HTML version deleted]]
______________________________________________ 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.
