Some fun with primes in ruby

primal.rb

require 'prime'

def list_primes_below(n)
  # List primes below argument
  return Prime::EratosthenesGenerator.new.take_while { |i| i <= n } 
end

def list_primes_count(n)
  # List argument number of primes
  return Prime::EratosthenesGenerator.new.take(n)
end

def prime_pair_combos_below(n)
  # All combinations of prime pairs for primes up to n
  primes = list_primes_below(n)
  primes.shift
  prime_pairs = [[2, 2]]
  return prime_pairs += primes.repeated_combination(2).to_a
end

def prime_pair_combos_count(n)
  # All combinations of prime pairs for n number of primes
  primes = list_primes_count(n)
  primes.shift
  prime_pairs = [[2, 2]]
  return prime_pairs += primes.repeated_combination(2).to_a
end

def prime_pair_permutes_below(n)
  # All permutations of primes below n
  primes = list_primes_below(n)
  primes.shift
  prime_pairs = [[2, 2]]
  return prime_pairs += primes.repeated_permutation(2).to_a
end

def prime_pair_permutes_count(n)
  # All permutations of n primes
  primes = list_primes_count(n)
  primes.shift
  prime_pairs = [[2, 2]]
  return prime_pairs += primes.repeated_permutation(2).to_a
end

def make_goldbach_hash_sum(prime_lists)
  goldbach_hash = Hash.new {|h,k| h[k]=[]}
  prime_lists.each do |prime_list|
    sum = prime_list.inject(:+)
    goldbach_hash[sum] << prime_list
  end
  return goldbach_hash
end

def make_goldbach_hash_avg(prime_lists)
  goldbach_hash = Hash.new {|h,k| h[k]=[]}
  prime_lists.each do |prime_list|
    sum = prime_list.inject(:+)
    avg = sum / prime_list.length
    goldbach_hash[avg] << prime_list
  end
  return goldbach_hash
end

def report_goldbach_hash(goldbach_hash)
  # generate a basic report
  report = ""
  goldbach_hash.sort.map do |number, prime_combos|
    report << "#{number}, "
    prime_combos.each do |primes|
      report << "#{primes}, "
    end
    report << "\n"
  end
  return report
end

def report_sums_table(n)
  ps = list_primes_count(n)
  ps.shift
  rows = ""
  ps.map do |p|
    ps.map do |q|
      rows << "#{p + q}, "
    end
    rows << "\n"
  end
  return rows
end
  
def report_avgs_table(n)
  ps = list_primes_count(n)
  ps.shift
  rows = ""
  ps.map do |p|
    ps.map do |q|
      rows << "#{(p + q) / 2}, "
    end
    rows << "\n"
  end
  return rows
end



# TODO: make some fancy reports. See examples below.

# Columnated Goldbach pairs

#  4, [ 2,  2],

#  6,, [ 3,  3], 
#  8,, [ 3,  5], [ 5,  3], 
# 10,, [ 3,  7], [ 5,  5], [ 7,  3], 
# 12,,         , [ 5,  7], [ 7,  5], 
# 14,, [ 3, 11],         , [ 7,  7], [11,  3], 
# 16,, [ 3, 13], [ 5, 11],         , [11,  5], [13,  3], 
# 18,,         , [ 5, 13], [ 7, 11], [11,  7], [13,  5], 
# 20,, [ 3, 17],         , [ 7, 13],         , [13,  7], [17,  3], 
# 22,, [ 3, 19], [ 5, 17],         , [11, 11],         , [17,  5], [19,  3], 
# 24,,           [ 5, 19], [ 7, 17], [11, 13], [13, 11], [17,  7], [19,  5], 
# 26,, [ 3, 23],         , [ 7, 19],         , [13, 13],         , [19,  7], [23,  3], 
# 28,,         , [ 5, 23],         , [11, 17],         , [17, 11],         , [23,  5], 
# 30,,         ,         , [ 7, 23], [11, 19], [13, 17], [17, 13], [19, 11], [23,  7], 
# 32,, [ 3, 29],         ,         ,         , [13, 19],         , [19, 13],         , [29,  3], 
# 34,, [ 3, 31], [ 5, 29],         , [11, 23],         , [17, 17],         , [23, 11], [29,  5], [31,  3], 
# 36,,         , [ 5, 31], [ 7, 29],         , [13, 23], [17, 19], [19, 17], [23, 13], [29,  7], [31,  5], 
# 38,,         ,         , [ 7, 31],         ,         ,         , [19, 19],         ,         , [31,  7], 
# 40,, [ 3, 37],         ,         , [11, 29],         , [17, 23],         , [23, 17], [29, 11],         , [37,  3], 
# 42,,         , [ 5, 37],         , [11, 31], [13, 29],         , [19, 23], [23, 19], [29, 13], [31, 11], [37,  5], 
# 44,, [ 3, 41],         , [ 7, 37],         , [13, 31],         ,         ,         ,         , [31, 13], [37,  7], [41,  3], 
# 46,, [ 3, 43], [ 5, 41],         ,         ,         , [17, 29],         , [23, 23], [29, 17],         ,         , [41,  5], [43,  3], 
# 48,,         , [ 5, 43], [ 7, 41], [11, 37],         , [17, 31], [19, 29],         , [29, 19], [31, 17], [37, 11], [41,  7], [43,  5], 
# 50,, [ 3, 47],         , [ 7, 43],         , [13, 37],         , [19, 31],         ,         , [31, 19], [37, 13],         , [43,  7], [47,  3], 
# ...

# Columnated avgs table

#     2,
#  2, 2,

#   ,  3,  5,  7, 11, 13, 17, 19, 23, 29, 31, 37, ...
#  3,  3,  4,  5,  7,  8, 10, 11, 13, 16, 17, 20,        
#  5,  4,  5,  6,  8 , 9, 11, 12, 14, 17, 18, 21,      
#  7,  5,  6,  7,  9, 10, 12, 13, 15, 18, 19, 22,     
# 11,  7,  8,  9, 11, 12, 14, 15, 17, 20, 21, 24,    
# 13,  8,  9, 10, 12, 13, 15, 16, 18, 21, 22, 25,   
# 17, 10, 11, 12, 14, 15, 17, 18, 20, 23, 24, 27, 
# 19, 11, 12, 13, 15, 16, 18, 19, 21, 24, 25, 28, 
# 23, 13, 14, 15, 17, 18, 20, 21, 23, 26, 27, 30, 
# 29, 16, 17, 18, 20, 21, 23, 24, 26, 29, 30, 33, 
# 31, 17, 18, 19, 21, 22, 24, 25, 27, 30, 31, 34, 
# 37, 20, 21, 22, 24, 25, 27, 28, 30, 33, 34, 37, 
# ...