min by columns

require 'test/unit'

def minByColumn(data, column_name, multiple = false)
  found_rows = []
  data.each { |row|
    next unless row.has_key?(column_name)
    if (found_rows.empty? or row[column_name] < found_rows.first[column_name])
      found_rows = [row]
    elsif (row[column_name] == found_rows.first[column_name])
      found_rows.push(row)
    end
  }
  return multiple ? found_rows : found_rows.first
end

def minByColumns(data, column_names, multiple = false)
  found_rows = minByColumn(data, column_names.shift, true)
  until (found_rows.length == 1 or column_names.empty?)
    new_found_rows = minByColumn(found_rows, column_names.shift, true)
    found_rows = new_found_rows unless new_found_rows.empty?
  end
  return multiple ? found_rows : found_rows.first
end

class MinByColumnTest < Test::Unit::TestCase
  def setup
    @simple_data = [
      {'a' => 0, 'b' => 1},
      {'a' =>  14, 'b' => -1}
    ]
    @mixed_data = [
      {'a' => 0, 'b' => 11},
      {'a' =>  14, 'b' => 34},
      {'a' => -1},
      {'b' => 3}
    ]
    @multi_data = [
      {'a' => 0, 'b' => 2},
      {'a' => 0, 'b' => 4}
    ]
    @dupe_data = [
      {'a' => 0, 'b' => 2},
      {'a' => 0, 'b' => 4},
      {'a' => 0, 'b' => 2}
    ]
  end

  def testMinByColumn
    assert_equal(minByColumn(@simple_data, 'a'), {'a' => 0, 'b' => 1})
    assert_equal(minByColumn(@simple_data, 'b'), {'a' => 14, 'b' => -1})
    assert_nil(minByColumn(@simple_data, 'c'))

    assert_equal(minByColumn(@mixed_data, 'a'), {'a' => -1})
    assert_equal(minByColumn(@mixed_data, 'b'), {'b' => 3})

    assert_nil(minByColumn([], 'b'))
  end

  def testMynByColumns
    assert_equal(minByColumns(@multi_data, ['a', 'b']), {'a' => 0, 'b' => 2})
    assert_equal(minByColumns(@multi_data, ['a', 'c', 'b']), {'a' => 0, 'b' => 2})
    assert_nil(minByColumns(@multi_data, ['c']))

    assert_equal(minByColumns(@dupe_data, ['a', 'b']), {'a' => 0, 'b' => 2})
  end
end