A better Ruby implementation of round decimal to nearest 0.5

Question

This seems horrible inefficient. Can someone give me a better Ruby way.

def round_value
  x = (self.value*10).round/10.0 # rounds to two decimal places
  r = x.modulo(x.floor) # finds remainder
  f = x.floor

  self.value = case
  when r.between?(0, 0.25)
    f
  when r.between?(0.26, 0.75)
    f+0.5
  when r.between?(0.76, 0.99)
    f+1.0
  end
end

Answer 1

Multiply the number by two.

round to whole number.

Divide by two.

(x*2.0).round / 2.0

In a generalized form, you multiply by the number of notches you want per whole number (say round to .2 is five notches per whole value). Then round; then divide by the same value.

(x*notches).round / notches

Answer 2

class Float
  def round_point5
    (self*2).round / 2.0
  end
end

A classic problem: this means you're doing integer rounding with a different radix. You can replace '2' with any other number.