Module: Factorise

Included in:
Integer
Defined in:
lib/factorise.rb,
lib/factorise/version.rb

Constant Summary collapse

VERSION = 
"0.4.0"

Instance Method Summary collapse

Instance Method Details

#factorise ⇒ Object

prime factors of a number



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# File 'lib/factorise.rb', line 6

def factorise
  number = self.to_s.dup.to_i
  factors = []

  primes_below = Prime.take_while { |p| p <= number / 2 }

  # keep if divisible
  primes_below.each do |p|
    until number % p != 0
      factors << p
      number = number / p
    end
  end

  # if no factors (=> num is prime) return num
  if factors.length == 0
    return [self]
  else
    return factors
  end
end

#factoriseh ⇒ Object

prime factors of a number as a hash



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# File 'lib/factorise.rb', line 29

def factoriseh
  array = self.factorise
  hash = {}

  # count each factor
  array.each do |factor|
    if hash.has_key? factor
      hash[factor] += 1
    else
      hash[factor] = 1
    end
  end

  return hash
end

#factorpairs ⇒ Object

factor pairs of a number (two numbers that multiply to get the number)



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# File 'lib/factorise.rb', line 54

def factorpairs
  num = self.to_s.dup.to_i
  pairs = []
  factors = num.nonprime

  # include or not include middle value
  if factors.length % 2 == 0
    firsthalf = factors.first(factors.length / 2)
  else
    firsthalf = factors.first((factors.length / 2) + 1)
  end

  # get pairs
  firsthalf.each_with_index do |factor, index|
    pairs[index] = [factor, num/factor]
  end

  return pairs
end

#nonprime ⇒ Object

non prime factors of a number (doesnt exclude primes)



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# File 'lib/factorise.rb', line 46

def nonprime
  num = self.to_s.dup.to_i

  # nice oneline
  return (1..num).select { |n| num % n == 0 }
end