# Ruby rounding? **URL:** \ **Category:** Ruby\ **Created:** [April 11, 2007, 8:18pm UTC](https://www.ruby-forum.com/t/ruby-rounding/91713 "2007-04-11T20:18:30Z")\ **Posts on this page:** 4\ **Page:** 1
**Author:** ![kyle\_s](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/k/f6c823/32.png) [@kyle\_s](https://www.ruby-forum.com/u/kyle_s)\ **Post date:** [April 11, 2007, 8:18pm UTC](https://www.ruby-forum.com/t/ruby-rounding/91713/1 "2007-04-11T20:18:30Z")
Something interesting came up at work concerning rounding. Notably, that the round procedure in [vb.net](http://vb.net) was good for stats (round to even), but since what the programmers expected (symmetric arithmetic rounding) was different, some edge cases were failing their tests. This got me thinking, what does Ruby use for rounding? It turns out (example below) it’s symmetric arithmetic rounding. But the methods in C’s math.h give the programmer a choice of which rounding method to use. Since there’s so much development going on in Ruby currently, maybe something like this could be/should be added. See [Rounding - Wikipedia](http://en.wikipedia.org/wiki/Rounding) for details on the methods ## –Kyle Using this array in several languages: [-5.0, -4.5, -4.0, -3.5, -3.0, -2.5, -2.0, -1.5, -1.0, -0.5, 0.0, 0.5, 1.0, 1.5, 2.0, 2.5, 3.0, 3.5, 4.0, 4.5] rounded: ruby [-5, -5, -4, -4, -3, -3, -2, -2, -1, -1, 0, 1, 1, 2, 2, 3, 3, 4, 4, 5] gcc [-5, -5, -4, -4, -3, -3, -2, -2, -1, -1, 0, 1, 1, 2, 2, 3, 3, 4, 4, 5] vbs (ugly but I had it on hand) [-5, -4, -4, -4, -3, -2, -2, -2, -1, 0, 0, 0, 1, 2, 2, 2, 3, 4, 4, 4] [vb.net](http://vb.net) (again ugly, but on hand) [-5, -4, -4, -4, -3, -2, -2, -2, -1, 0, 0, 0, 1, 2, 2, 2, 3, 4, 4, 4] ---
**Author:** ![kyle\_s](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/k/f6c823/32.png) [@kyle\_s](https://www.ruby-forum.com/u/kyle_s)\ **Post date:** [April 11, 2007, 10:30pm UTC](https://www.ruby-forum.com/t/ruby-rounding/91713/2 "2007-04-11T22:30:44Z")
On Apr 11, 11:17 am, “Kyle S.” [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) wrote: > Since there’s so much development going on in Ruby currently, maybe > something like this could be/should be added. You could always create your own :). Here is a something that I put together. There may be a better method. The weird thing in the code with comparing the remainder to 1e-9 is to deal with floating point precision issues. This may or may not be appropriate… I’m not a rounding expert but it’s worked in applications that I developed. Anyway, here it is: class Numeric def even\_round() if ((self.truncate % 2 == 0) and ((self.remainder(1).abs - 0.5).abs \< 1e-9)) # integer portion is even and on 0.5 threshold self.truncate else # integer portion is odd or not on 0.5 threshold self.round end end end irb(main):012:0\> a = [-5.0, -4.5, -4.0, -3.5, -3.0, -2.5, -2.0, -1.5, -1.0, -0.5, 0.0, 0.5, 1.0, 1.5, 2.0, 2.5, 3.0, 3.5, 4.0, 4.5] =\> [-5.0, -4.5, -4.0, -3.5, -3.0, -2.5, -2.0, -1.5, -1.0, -0.5, 0.0, 0.5, 1.0, 1.5, 2.0, 2.5, 3.0, 3.5, 4.0, 4.5] irb(main):013:0\> a.map {|e| e.even\_round} =\> [-5, -4, -4, -4, -3, -2, -2, -2, -1, 0, 0, 0, 1, 2, 2, 2, 3, 4, 4, 4] ---
**Author:** ![kyle\_s](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/k/f6c823/32.png) [@kyle\_s](https://www.ruby-forum.com/u/kyle_s)\ **Post date:** [April 11, 2007, 11:21pm UTC](https://www.ruby-forum.com/t/ruby-rounding/91713/3 "2007-04-11T23:21:51Z")
On Apr 11, 2:25 pm, removed\_email\_address@domain.invalid wrote: > On Apr 11, 11:17 am, “Kyle S.” [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) wrote > > You could always create your own :). Here is a something that I put > together. There may be a better method. The weird thing in the code > with comparing the remainder to 1e-9 is to deal with floating point > precision issues. This may or may not be appropriate… I’m not a > rounding expert but it’s worked in applications that I developed. I could be wrong, but I think this is what the constant Float::EPSILON is for. Where I’m sitting it’s 2.22044604925031e-16. Chris ---
**Author:** ![kyle\_s](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/k/f6c823/32.png) [@kyle\_s](https://www.ruby-forum.com/u/kyle_s)\ **Post date:** [April 12, 2007, 7:45am UTC](https://www.ruby-forum.com/t/ruby-rounding/91713/4 "2007-04-12T07:45:21Z")
On Apr 11, 2:19 pm, “Chris S.” [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) wrote: > I could be wrong, but I think this is what the constant Float::EPSILON > is for. Where I’m sitting it’s 2.22044604925031e-16. Excellent - thanks for the info.