From: Bernard Kenik <renard@...>
Date: 2006-12-06T07:16:27+09:00
Subject: Re: number format

You can use the number.round method, but this doesn't take a number of 
decimal places.

To round 1.234 to 1.23 use this code:
x = 1.234
x = x * 100 # -> 123.4
x = x.round -> 123
x = x / 100.0 => 1.23

At least, that's the best method I can find from the Ruby docs...

Dan

Li Chen wrote:
Hi all,

I have a number, for example, 1.123456789. What is the Ruby way to
change it into whatever number of floating points such as 1.12,
1.123,1.1234568 or 1.12345679.

Thanks,

Li

class Float
  def places(places)
    (self * 10 ** places).truncate / 10.0 ** places
  end
end

1.123456789.places(5)   => 1.12345

you can use round instead of truncate if you want to round off

alternate method
class Float
  def place(places)
    sprintf("%0.#{places}f", self).to_f
  end
end

not sure which method is most efficient