Module: Random::ArrayExtensions

Included in:
Array
Defined in:
lib/standard/facets/random.rb

Overview

Random extensions for Array class.

Instance Method Summary collapse

Instance Method Details

#at_rand ⇒ Object

Return a random element from the array.

[1, 2, 3, 4].at_rand           #~> 2
[1, 2, 3, 4].at_rand           #~> 4



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# File 'lib/standard/facets/random.rb', line 141

def at_rand
  at(Random.number(size))
end

#at_rand! ⇒ Object

Same as #at_rand, but acts in place removing a random element from the array.

a = [1,2,3,4]
a.at_rand!       #~> 2
a                #~> [1,3,4]



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# File 'lib/standard/facets/random.rb', line 152

def at_rand!
  return delete_at( Random.number( size ) )
end

#pick(n = nil) ⇒ Object

Similar to #at_rand, but will return an array of randomly picked exclusive elements if given a number.



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# File 'lib/standard/facets/random.rb', line 158

def pick(n=nil)
  if n
    a = self.dup
    a.pick!(n)
  else
    at(Random.number(size))
  end
end

#pick!(n = nil) ⇒ Object

Similar to #at_rand!, but given a number will return an array of exclusive elements.



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# File 'lib/standard/facets/random.rb', line 169

def pick!(n=nil)
  if n
    if n > self.size
      r = self.dup
      self.replace([])
      r
    else
      r = []
      n.times { r << delete_at(Random.number(size)) }
      r
    end
  else
    delete_at(Random.number(size))
  end
end

#rand_index ⇒ Object

Random index.



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# File 'lib/standard/facets/random.rb', line 187

def rand_index
  Random.number(size)
end

#rand_subarrays(n = 1) ⇒ Object

Generates random subarrays. Uses random numbers and bit- fiddling to assure performant uniform distributions even for large arrays.

a = *1..5
a.rand_subarrays(2) #=> [[3, 4, 5], []]
a.rand_subarrays(3) #=> [[1], [1, 4, 5], [2, 3]]

CREDIT: Michael Kohl

Raises:

  • (ArgumentError) 


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# File 'lib/standard/facets/random.rb', line 227

def rand_subarrays(n=1)
  raise ArgumentError, "negative argument" if n < 0
  (1..n).map do
    r = rand(2**self.size)
    self.select.with_index { |_, i| r[i] == 1 }
  end
end

#rand_subset(number = nil, exclusive = true) ⇒ Object

Returns a random subset of an Array. If a number of elements is specified then returns that number of elements, otherwise returns a random number of elements upto the size of the Array.

By defualt the returned values are exclusive of each other, but if exclusive is set to false, the same values can be choosen more than once.

When exclusive is true (the default) and the number given is greater than the size of the array, then all values are returned.

[1, 2, 3, 4].rand_subset(1)        #~> [2]
[1, 2, 3, 4].rand_subset(4)        #~> [2, 1, 3, 4]
[1, 2, 3, 4].rand_subset           #~> [1, 3, 4]
[1, 2, 3, 4].rand_subset           #~> [2, 3]



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# File 'lib/standard/facets/random.rb', line 209

def rand_subset(number=nil, exclusive=true)
  number = Random.number(size) unless number
  number = number.to_int
  #return self.dup if (number >= size and exlusive)
  return sort_by{rand}.slice(0,number) if exclusive
  ri =[]; number.times { |n| ri << Random.number(size) }
  return values_at(*ri)
end

#shuffle ⇒ Object

Randomize the order of an array.

[1,2,3,4].shuffle  #~> [2,4,1,3]



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# File 'lib/standard/facets/random.rb', line 239

def shuffle
  dup.shuffle!
  #sort_by{Random.number}
end

#shuffle! ⇒ Object

As with #shuffle but modifies the array in place. The algorithm used here is known as a Fisher-Yates shuffle.

a = [1,2,3,4]
a.shuffle!

a  #~> [2,4,1,3]

CREDIT Niel Spring



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# File 'lib/standard/facets/random.rb', line 253

def shuffle!
  s = size
  each_index do |j|
    i = Random.number(s-j)
    #self[j], self[j+i] = self[j+i], self[j]
    tmp = self[j]
    self[j] = self[j+i]
    self[j+i] = tmp
  end
  self
end