From: Chris Shea <cmshea@...>
Date: 2007-12-18T04:25:02+09:00
Subject: Re: dividing by two and rounding up

On Dec 17, 11:42 am, Tom Norian <tomnor...@yahoo.com> wrote:
> Hey all...I am hoping for a tip
>
> I have a table I want to lay out dynamcially in rails where if a game
> has 6 periods the first 3 periods will be in the first column and the
> 4-6 in the second column.  If someone picks an odd number of periods ,
> say 5, I want the 1-3 in the first column and 4 and 5 in the second.
>
> I have figured out how to iterate through IF I could get 5/2 to yield me
> 3.
>
> How do I divide a number (integer) by 2 and get a result that is like:
>
> 5/2 I want 3
>  6/2 I want 3
> 7/2 I want 4
>
> I'm thinking perhaps I could test for oddness then add one to the result
> if odd, but that seems kinda a lot of lines for something so simple.
>
> half_periods = 0
> if num_periods%2 == 1
>   half_periods = num_periods/2 +1
> else
>   half_periods = num_periods/2
> end
>
> Is there a better way?
> --
> Posted viahttp://www.ruby-forum.com/.

Here's a few ways:

require "test/unit"

PERIODS  = [1,2,3,4,5,6,7,8,9,10]
PER_HALF = [1,1,2,2,3,3,4,4,5,5]

class TestPeriods < Test::Unit::TestCase
  def test_div_two_plus_mod_two
    assert_equal(PER_HALF, PERIODS.map {|period| period / 2 + period %
2})
  end

  def test_plus_mod_two_div_two
    assert_equal(PER_HALF, PERIODS.map {|period| (period + period %
2) / 2})
  end

  def test_plus_one_div_two
    assert_equal(PER_HALF, PERIODS.map {|period| (period + 1) / 2})
  end

  def test_div_2_ceil
    assert_equal(PER_HALF, PERIODS.map {|period| (period / 2.0).ceil})
  end

  def test_plus_1_div_two_floor
    assert_equal(PER_HALF, PERIODS.map {|period| ((period + 1.0) /
2).floor})
  end

  def test_div_2_round
    assert_equal(PER_HALF, PERIODS.map {|period| (period /
2.0).round})
  end
end