From: Simon Strandgaard <neoneye@...>
Date: 2004-08-14T20:52:20+09:00
Subject: Re: [RCR] Array#transpose way of dealing with nil's

On Saturday 14 August 2004 13:20, Simon Strandgaard wrote:
> At the moment #transpose rejects nil values.
> It could be really nice if one tell #transpose that it
> whenever it meets a nil entry.. that a nil value also should be outputted.
>
> [[1, 2], [3, 4], nil, [5, 6]].transpose(true)
> #=> [[1, 3, nil, 5], [2, 4, nil, 6]]
>
>
> I often find myself needing this for unittesting.. like this
>
> def generic_test_bracket_matcher(str, inpos, expected_xs, expected_ys)
>   res = inpos.map {|p| str.match_bracket(p) }
>   ys, xs = res.transpose    # BOOM: this doesn't like nil elements
>   assert_equal(expected_xs, xs)
>   assert_equal(expected_ys, ys)
> end
>
> --
> Simon Strandgaard

here is a possible implementation

bash-2.05b$ ruby test_transpose.rb
Loaded suite test_transpose
Started
...
Finished in 0.004324 seconds.

3 tests, 3 assertions, 0 failures, 0 errors
bash-2.05b$ expand -t2 test_transpose.rb
require 'test/unit'

class Array
  def transpose_except(*elements_to_exclude)
    n = 0
    self.each do |i|
      n = [n, i.size].max if i.kind_of?(Array)
    end
    ary = self.map do |i|
      next [i]*n if elements_to_exclude.member?(i)
      i
    end
    ary.transpose
  end
end

class TestTranspose < Test::Unit::TestCase
  def test_trans1
    ary = [[1, 2], [3, 4], [5, 6]]
    assert_equal([[1, 3, 5], [2, 4, 6]],
      ary.transpose_except)
  end
  def test_trans2
    ary = [[1, 2], nil, [3, 4]]
    assert_equal([[1, nil, 3], [2, nil, 4]],
      ary.transpose_except(nil))
  end
  def test_trans3
    ary = [[1, 2], :a, [3, 4], :b, [5, 6]]
    assert_equal([[1, :a, 3, :b, 5], [2, :a, 4, :b, 6]],
      ary.transpose_except(:a, :b))
  end
endbash-2.05b$

--
Simon Strandgaard