Boolean comparison of array of strings in Ruby

Question

I've got an array in Ruby that essentially represents a square boolean matrix. Dots represent zeroes, while any other character represents ones. Example:

irb(main):044:0> g
=> [".b", "m."] # This grid has two '1' values and two '0' values.

I'd like to perform a specified logical operation (say, OR) on this array with another similar array to get a third result. For example, if h is ["q.", "r."], then something akin to g.perform_or(h) should yield a new array ["qb", "r."]. (The choice of r to represent the result of 'm' || 'r' is arbitrary and not relevant; any other non-'.' character can be there.)

How might I do this?

Edit: I made an error in my example. Apologies!

If '.' == 0 and /[^.]/ == 1, your example of an or function is wrong. — EmFi
– EmFi, Commented Nov 20, 2009 at 4:39
So, outside of the actual answer I'm curious about what you're doing with this? Sounds interesting! — Chuck Vose
– Chuck Vose, Commented Nov 20, 2009 at 5:40
If you change the problem statement, you waste the time of all those who tried to answer your question before you change it. — Chirantan
– Chirantan, Commented Nov 20, 2009 at 14:35

glenn mcdonald · Accepted Answer · 2009-11-20 05:04:25Z

6

For OR:

g.zip(h).map {|gx,hx| (0...gx.size).map {|i| [gx[i..i],hx[i..i]].any? {|cell| cell != "."} ? "x" : "."}.join}

For AND just change the "any?" to "all?".

answered Nov 20, 2009 at 5:04

glenn mcdonald

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3 Comments

Chuck Vose Over a year ago

I was trying to understand this and I'm not getting the same result as specified above. I'm getting ['xx', 'x.']. Even if you had transposed . and x it should look like ['xx', '.x']. Am I wrong about this?

Chirantan Over a year ago

Me too. It should actually look like ['..', 'x.']

Chuck Vose Over a year ago

glenn deserves a double bump then for finding the right answer and the right question :P

Jörg W Mittag · Accepted Answer · 2010-06-02 12:36:15Z

Man, this one has been gathering dust on my disk for a loong time:

class String
  def to_bool; return chars.map {|c| if c == '.' then false else c end } end
  def from_bool; return self end
end

class TrueClass;  def from_bool; return 't' end end
class FalseClass; def from_bool; return '.' end end

class Array
  def to_bool;   map(&:to_bool) end
  def from_bool; map {|row| row.map(&:from_bool).join} end

  def |(other)
    to_bool.zip(other.to_bool).inject([]) {|row, (l, r)|
      row << l.zip(r).inject([]) {|col, (l, r)|
        col << (l || r).from_bool
      }
    }
  end

  def &(other)
    to_bool.zip(other.to_bool).inject([]) {|row, (l, r)|
      row << l.zip(r).inject([]) {|col, (l, r)|
        col << (l && r).from_bool
      }
    }
  end
end

Here's a (rather incomplete) testsuite:

require 'test/unit'
class TestLogicMatrix < Test::Unit::TestCase
  def test_to_bool
    assert_equal [['a', false], [false, 'z']], ['a.', '.z'].to_bool
  end
  def test_from_bool
    assert_equal ['a.', 'tz'], [['a', false], [true, 'z']].from_bool
  end
  def test_that_OR_works
    assert_equal ['qb', 'm.'], (['.b', 'm.'] | ['q.', 'r.']).from_bool
  end
  def test_that_AND_works
    assert_equal ['..', 'r.'], (['.b', 'm.'] & ['q.', 'r.']).from_bool
  end
end

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