From: Gavin Kistner <gavin.kistner@...>
Date: 2006-10-14T00:48:17+09:00
Subject: Re: How do I round off a float to x decimal places

From: Jatinder Singh [mailto:jatinder.saundh@gmail.com] 
> This might be a very naive question but I looked through ruby:Float
> documentation for a method which round off's a float number 
> to x decimal
> places with no luck.

To get the result as a number (which, due to floating point precision,
might not be an exact representation of what you wanted):
class Numeric
  def round_to( decimals )
    factor = 10 ** decimals
    ( self * factor ).round  * 1.0 / factor
  end
end

(Bonus - works with "negative" decimals, to round to tens or hundreds or
thousands.)

To get the result as a string, which is probably what you really wanted:
class Numeric
  def round_to_string( decimals )
    "%.#{decimals}f" % self
  end
end