about_arrays.rb

require File.expand_path(File.dirname(__FILE__) + '/neo')

class AboutArrays < Neo::Koan
  def test_creating_arrays
    empty_array = Array.new
    assert_equal Array, empty_array.class
    assert_equal 0, empty_array.size
  end

  def test_array_literals
    array = Array.new
    assert_equal [], array

    array[0] = 1
    assert_equal [1], array

    array[1] = 2
    assert_equal [1, 2], array

    #Appending a value in the array at last position with << operator
    array << 333
    assert_equal [1,2, 333], array
  end

  def test_accessing_array_elements
    array = [:peanut, :butter, :and, :jelly]

    assert_equal :peanut, array[0]
    assert_equal :peanut, array.first
    assert_equal :jelly, array[3]
    assert_equal :jelly, array.last

    #Negative index refers to the relative position in the end of the array -1 is the last element of the array, -2 the next to the last etc...
    assert_equal :jelly, array[-1]
    assert_equal :butter, array[-3]
  end

  def test_slicing_arrays
    #TODO: READ http://thepaulrayner.com/blog/2013/02/07/array-slicing-in-ruby/
    array = [:peanut, :butter, :and, :jelly]

    assert_equal [:peanut], array[0,1]
    assert_equal [:peanut, :butter], array[0,2]
    assert_equal [:and, :jelly], array[2,2]
    assert_equal [:and, :jelly], array[2,20]
    assert_equal [], array[4,0]
    assert_equal [], array[4,100]
    assert_equal nil, array[5,0]
  end

  def test_arrays_and_ranges
    assert_equal Range, (1..5).class
    assert_not_equal [1,2,3,4,5], (1..5)
    assert_equal [1,2,3,4,5], (1..5).to_a # Two dots indicates that the last element of the range is included in the array
    assert_equal [1,2,3,4], (1...5).to_a # Three dots indicates that the last element of the range is not included
  end

  def test_slicing_with_ranges
    array = [:peanut, :butter, :and, :jelly]

    assert_equal [:peanut, :butter, :and], array[0..2]
    assert_equal [:peanut, :butter], array[0...2]
    assert_equal [:and, :jelly], array[2..-1] # -1 is the last element of the array
  end

  def test_pushing_and_popping_arrays
    array = [1,2]
    array.push(:last)

    assert_equal [1,2,:last], array

    popped_value = array.pop #pop or remove the last element of the given array
    assert_equal :last, popped_value
    assert_equal [1,2], array
  end

  def test_shifting_arrays
    array = [1,2]
    array.unshift(:first) # add to the start of the list :first vale

    assert_equal [:first, 1, 2], array

    shifted_value = array.shift # removes from the start of the list the :first value, using shift(n) will remove as much elements from start as indicated and return then
    assert_equal :first, shifted_value
    assert_equal [1,2], array

    array.unshift(:pepe)

    shifted_value = array.shift(2) # when are more than one element to shift it returns a list of the shifted elements
    assert_equal([:pepe, 1], shifted_value)
  end

end