Cartesian

The Cartesian module provide methods for the calculation of the cartesian producted between two enumerable objects.

It can also be easily mixed in into any enumerable class, i.e. any class with Enumerable module mixed in. Notice that the names of the methods for mixin are different.

Module:

  Cartesian::product(foo, bar)

Mixin:

  foo.cartesian( bar )

The module is automatically mixed in Array class.

Author

Adriano MITRE

Example

as module

  require 'cartesian'
  foo = [1, 2]
  bar = ["a", "b"]
  Cartesian::product(foo, bar) #=> [[1, "a"], [1, "b"], [2, "a"], [2, "b"]]

as mixin

  require 'cartesian'
  foo = [1, 2]
  bar = ["a", "b"]
  foo.cartesian(bar)  #=> [[1, "a"], [1, "b"], [2, "a"], [2, "b"]]

Constants

VERSION: Unfortunately, as of now, the version data must be replicated in ../cartesian.rb, due to a mix of newgem versions, each requiring a different one. Not DRY :P

Public Class Methods

joined_product(first, second) click to toggle source

Behaves as product, except for the elements are joined.

  Cartesian::joined_cartesian( [1,2], %w(A B) ) #=> ["1A", "1B", "2A", "2B"]

or, if mixed in into Array,

  [1,2].joined_cartesian %w(A B) #=> ["1A", "1B", "2A", "2B"]

    # File lib/cartesian.rb, line 65
65:   def Cartesian.joined_product(first, second)
66:     product(first, second).map {|pair| pair.join }
67:   end

product(first, second) click to toggle source

Produces the cartesian product of self and other. The result is an array of pairs (i.e. two-element arrays).

  Cartesian::product( [1,2], %w(A B) ) #=> [[1, "A"], [1, "B"], [2, "A"], [2, "B"]]

or, if mixed in into Array,

  [1,2].cartesian %w(A B) #=> [[1, "A"], [1, "B"], [2, "A"], [2, "B"]]

    # File lib/cartesian.rb, line 53
53:   def Cartesian.product(first, second)
54:     first.x(second).to_a
55:   end

Public Instance Methods

**(fixnum) click to toggle source

Concise way of iterating multi-dimensionally over the same array or range.

For instance,

  for x,y,z in [0,1]**3
    puts [x, y, z].join(',')
  end

produces the following output

  0,0,0
  0,0,1
  0,1,0
  0,1,1
  1,0,0
  1,0,1
  1,1,0
  1,1,1

It also works with Range objects.

     # File lib/cartesian.rb, line 143
143:   def **(fixnum)
144:     if fixnum < 0
145:       raise ArgumentError, "negative power"
146:     elsif fixnum == 0
147:       return []
148:     elsif fixnum == 1
149:       return self
150:     else
151:       iter = CartesianIterator.new(self, self)
152:       (fixnum-2).times do
153:         iter.product!(self)
154:       end
155:       iter
156:     end
157:   end

Also aliased as: power!

cartesian(other) click to toggle source

Alias for: x

joined_cartesian(other) click to toggle source

Cartesian.joined_product for mixin.

    # File lib/cartesian.rb, line 71
71:   def joined_cartesian(other)
72:     Cartesian.joined_product(self, other)
73:   end

left_product(other) click to toggle source

     # File lib/cartesian.rb, line 112
112:   def left_product(other)
113:     case other
114:     when CartesianIterator
115:       other.right_product(self)
116:     else
117:       CartesianIterator.new(other, self)
118:     end
119:   end

power!(fixnum) click to toggle source

Alias for: **

right_product(other) click to toggle source

Alias for: x

x(other) click to toggle source

Convenient way of iterating over the elements. Preferable when the cartesian product array is not needed, for the consumption of memory is fixed and very small, in contrast with the exponential memory requirements of the conventional approach.

  for row, col in (1..10).x(1..30)
    Matrix[row, col] = row**2 + col**3
  end

Of course, calls can be chained as in

  for x, y, z in (1..10).x(1..10).x(1..10)
    # ... do something ...
  end

Beware that both self and other must implement to_a, i.e., be convertible to array.

     # File lib/cartesian.rb, line 101
101:   def x(other)
102:     case other
103:     when CartesianIterator
104:       other.left_product(self)
105:     else
106:       CartesianIterator.new(self, other)
107:     end
108:   end

Also aliased as: cartesian, right_product

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