Round floats to the nearest X

core_ext | float | ruby July 18 2007

For those pesky times when whole numbers just won’t cut it, but you only want some precision.

7.7.round(0.5)   #=> 7.5
7.95.round(0.5)  #=> 8
8.2.round(1.5)   #=> 7.5
8.3.round(1.5)   #=> 9

The magic, courtesy of Daniel Morrison:

class Float
  def round(round_to = 1.0)
    mod = self % round_to
    rounded = self - mod + (mod >= round_to/2.0 ? round_to : 0)
    rounded % 1 == 0 ? rounded.to_i : rounded
  end
end

Note that do to some quirks with Ruby’s handling of floats, you won’t get what you expect in some situations:

3.5.round(0.2)   #=> 3.4, instead of 3.6
posted by brandon
comments feed

2 comments

  1. This is a little more complicated, but it correctly rounds results:

    class Float
  alias_method :old_round, :round unless method_defined?(:old_round)
  def round(round_to = 1.0)
    scaled = self / round_to
    rounded = scaled.old_round * round_to
    rounded % 1 == 0 ? rounded.to_i : rounded
  end
end
    Matt Jones Matt Jones
    July 18, 2007 at 03:08 PM

  2. What about:

    require 'bigdecimal'

class Float
  def round(to = 0)
    rounded = BigDecimal(self.to_s).round(to)
    to == 0 ? rounded.to_i : rounded
  end
end
    Dan Kubb Dan Kubb
    December 06, 2007 at 11:07 PM

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