[R] strange floor rounding

[Duncan Murdoch]

On 09/07/2010 10:27 AM, Trafim Vanishek wrote:
> Thanks everybody for referring me to FAQ 7.31 but I don't see how to solve
> it.
> I am giving a concrete number and I need to get 58 not 57. Seems, there is
> no way?
>   
You aren't giving a "concrete number".  You're giving a string of three 
characters, which R interprets as a number that's a little bit less than 
0.58, because
there is no way to represent the number 0.58 in the floating point 
format that R uses.  So it is calculating the right answer.

If you want to work with exact 2 decimal place values, you should not 
use floating point storage.  One alternative is to work with integers 
equal to 100 times the value you want, and then divide by 100 at the 
very end of the operation for printing.

Duncan Murdoch
> On Fri, Jul 9, 2010 at 4:05 PM, David Winsemius <dwinsemius at comcast.net>wrote:
>
> >
> > On Jul 9, 2010, at 9:46 AM, Trafim Vanishek wrote:
> >
> >  Dear all,
> >>
> >> might seem and easy question but I cannot figure it out.
> >>
> >> floor(100*(.58))
> >> [1] 57
> >>
> >> where is the trick here?
> >>
> >
> > FAQ 7.31
> >
> >
> > And how can I end up with the right answer?
> >>
> >
> > Define right, please. (There have been several questions in the last week
> > for which FAQ 7.31 was the answer and some of the responses had useful
> > links.)
> >
> > --
> > David Winsemius, MD
> > West Hartford, CT
> >
> >
>
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>
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