Dividing by two and rounding up

Ruby
1

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?

2

Tom N. wrote:

Is there a better way?

Something like this ?

((num_periods + 0.5)/2).round

3

On Dec 17, 2007, at 10:42 , Tom N. wrote:

half_periods = 0
if num_periods%2 == 1
half_periods = num_periods/2 +1
else
half_periods = num_periods/2
end

(5/2.0).ceil

Corey

4

Thanks guys.

5

On Dec 17, 11:42 am, Tom N. [email protected] wrote:

How do I divide a number (integer) by 2 and get a result that is like:
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 another way

half_periods = periods / 2 + periods % 2

HTH,
Chris

6

On Dec 17, 11:42 am, Tom N. [email protected] wrote:

How do I divide a number (integer) by 2 and get a result that is like:
half_periods = num_periods/2 +1
else
half_periods = num_periods/2
end

irb(main):012:0> 1.upto(5){ |i|
irb(main):013:1* val = (i/2.0).ceil
irb(main):014:1> puts “#{i}/2 → #{val}”
irb(main):015:1> }
1/2 → 1
2/2 → 1
3/2 → 2
4/2 → 2
5/2 → 3

7

Tom N. wrote:

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

(5/2.0).ceil
=> 3

(6/2.0).ceil
=> 3

(7/2.0).ceil
=> 4

HTH,
Sebastian

8

This is Ruby so fast is not what you are going for, but I can’t help
pointing out that (n+1)>>1 many be the ‘fastest’ option.

9

On Dec 17, 2007 7:51 PM, Lionel B. [email protected]
wrote:

Is there a better way?

Something like this ?

(num_periods / 2.0).ceil

or (num_periods + 1)/2 if we want to stay with integers.

10

On Dec 17, 12:42 pm, Tom N. [email protected] wrote:

How do I divide a number (integer) by 2 and get a result that is like:
half_periods = num_periods/2 +1
else
half_periods = num_periods/2
end

Is there a better way?

Posted viahttp://www.ruby-forum.com/.

Use floats and #round.

def div(x, y)
(x.to_f/y).round
end

div(5,2) # => 3
div(6,2) # => 3
div(7,2) # => 4

Regards,
Jordan

11

On Dec 18, 2007 12:12 AM, Tom N. [email protected] wrote:

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

(n+1)/2

irb(main):001:0> (1…10).map {|i| [i, (i+1)/2]}
=> [[1, 1], [2, 1], [3, 2], [4, 2], [5, 3], [6, 3], [7, 4], [8, 4],
[9, 5], [10, 5]]

martin

12

On Dec 17, 11:42 am, Tom N. [email protected] wrote:

How do I divide a number (integer) by 2 and get a result that is like:
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

13

Tom N. wrote:

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

Here’s another way, one integer division, but 2 instructions:

a = 5.divmod(2)
result = a[1] + a[2]

Best regards,

Jari W.

14

Corey J. schrieb:

yield me
if odd, but that seems kinda a lot of lines for something so simple.
Corey
(5+1) / 2

15

Why not get the arrays:

irb(main):022:0> a
=> [1, 2, 3, 4, 5, 6]
irb(main):023:0> a.slice(0,3)
=> [1, 2, 3]
irb(main):024:0> a.slice(3,3)
=> [4, 5, 6]
irb(main):025:0> b
=> [1, 2, 3, 4, 5]
irb(main):026:0> b.slice(0,3)
=> [1, 2, 3]
irb(main):027:0> b.slice(3,3)
=> [4, 5]

then loop over them creating the columns.

-corey

On Dec 17, 2007 4:12 PM, Jari W.

16

Or, better yet

require ‘enumerator’

irb(main):036:0> a.each_slice(3) do |slice|
irb(main):037:1* puts slice.join(", “)
irb(main):038:1> end
1, 2, 3
4, 5, 6
=> nil
irb(main):039:0> b.each_slice(3) do |slice|
irb(main):040:1* puts slice.join(”, ")
irb(main):041:1> end
1, 2, 3
4, 5

This way, you don’t have to worry about it, since you are always
grabbing the first three.