A way to round Floats down

Question

Float round rounds it up or down. I always need it to round down.

I have the solution but i dont really like it... Maybe there is a better way.

This is what i want:

1.9999.round_down(2) 
#=> 1.99
1.9901.round_down(2)
#=> 1

I came up with this solution but i would like to know if there is a better solution(I dont like that i convert the float twice). Is there already a method for this? Because I found it pretty strange that I couldnt find it.

class Float
  def round_down(n=0)
    ((self * 10**n).to_i).to_f/10**n 
  end
end

Thanks.

Answer 1

1.9999.to_i
#=> 1
1.9999.floor
#=> 1

answered 1 sec ago fl00r

"%.2f" % 1.93213
#=> 1.93

@kimmmo is right.

class Float
  def round_down(n=0)
    self.to_s[/\d+\.\d{#{n}}/].to_f
  end
end

Answer 2

Based on answer from @kimmmo this should be a little more efficient:

class Float
  def round_down n=0
  s = self.to_s
  l = s.index('.') + 1 + n
  s.length <= l ? self : s[0,l].to_f
  end
end

1.9991.round_down(3)
 => 1.999
1.9991.round_down(2)
 => 1.99
1.9991.round_down(0)
 => 1.0
1.9991.round_down(5)
 => 1.9991

or based on answer from @steenslag, probably yet more efficient as there is no string conversion:

class Float
  def round_down n=0
    n < 1 ? self.to_i.to_f : (self - 0.5 / 10**n).round(n)
  end
end