how to set 2 variables to either 1 or 0 based on a 3rd variables value

I have a variable that will have the following values:

blah = # 1, 0, or -1

Now I want to set these two variables:

up

down

To either 1 or 0 based on the value of 'blah'.

If blah is 1, then up = 1 and down = 0, if blah is -1 then down = 1 and up = 0

If blah is 0, then both are 0.

How can you do this the ruby way w/o so 开发者_开发知识库many if checks?

Solution 1

up, down =
case blah
when 1; [1, 0]
when 0; [0, 0]
when -1; [0, 1]
end

Solution 2 (Inspired by mu is too short)

up, down = [[0, 0], [1, 0], [0, 1]][blah]

A variant of sawa's and SirDarius's that allows blah to be greater than, less than, or equal to zero rather than just -1, 0, or 1:

def mapper(x)
    h = {
        -1 => [0, 1],
         0 => [0, 0],
         1 => [1, 0]
    }
    h[x <=> 0]
end

up, down = mapper(blah)

Note that Fixnum's <=> operator is specified to return -1, 0, or 1 (or nil of course):

Returns -1, 0, +1 or nil depending on whether fix is less than, equal to, or greater than numeric.

So using <=> is a safe way to implement the signum function for Fixnum.

According to your initial specification, the following code worked:

up = 0
down = -blah

EDIT:

Here is a creative way to achieve the desired result using a Hash:

states = { -1 => [0,1], 0 => [0,0], 1 => [1,0] }
up, down = states[blah]

up = blah == 1 ? 1 : 0
down = blah == -1 ? 1 : 0

I don't think this is ruby-specific... something like

up = blah != -1
down = blah != 1

I assume you mean that up should be 1 when blah is 1.

Yet another way to do it:

up, down = [0, blah].max, [0, -blah].max

Reset both answers to 0 and then adjust as necessary

up, down = 0, 0
up = 1 if blah > 0
down = 1 if blah < 0

class Integer
  def up?
    self == 1
  end

  def down?
    self == -1
  end
end

x = 1
x.up? # => true