Ruby each block, does not return value

Question

This following Code doesn't work, the Problem is inside of the calc_fitness method, the each block does not return an value, and i dont know why

# takes an array, splices them into groups of 2 and returns a sum of values read from the matrix
def calc_fitness(hypothesis_arr)
   hypothesis_arr.each_slice(2).to_a.map{|v| $distances[v.first,v.last]}
end

def main

  # filling the matrix, with random values
  $distances = create_sym_matrix
  p calc_fitness((0..99).to_a) 
end

main
# => [67,67,67,67....67,] #these should not be the same, which means i  the block alway returns the same value. Why?

everything in ruby returns a value. it just so happens the return value for main is nil because the return value from hypothesis_arr.each_slice(2).each{|v| $distances[v.first,v.last]} is nil. You can recreate this by simply (0..99).to_a.each_slice(2).each{} #=> nil — engineersmnky
– engineersmnky, Commented Nov 7, 2017 at 15:18
Be extremely careful when using global variables like $distances, which is what the $ prefix means. These can render otherwise ordinary code completely unmaintainable in a hurry. Likewise there is no reason for a main method, Ruby already has a main context for this purpose, that is code outside of any class, module or method definition. — tadman
– tadman, Commented Nov 7, 2017 at 19:16

Derek Wright · Accepted Answer · 2017-11-07 16:44:16Z

This happens because each returns itself (an instance of Enumerator) and each_slice return nil.

https://ruby-doc.org/core/Enumerable.html#method-i-each_slice

You could try changing the each to a map

To simplify and get a visual of what was generated, I used:

(1..99).to_a.each_slice(2).map { |v| { first: v.first, last: v.last } }
=> [{:first=>1, :last=>2}, {:first=>3, :last=>4}, {:first=>5, :last=>6}, {:first=>7, :last=>8}, {:first=>9, :last=>10}, {:first=>11, :last=>12}, {:first=>13, :last=>14}, {:first=>15, :last=>16}, {:first=>17, :last=>18}, {:first=>19, :last=>20}, {:first=>21, :last=>22}, {:first=>23, :last=>24}, {:first=>25, :last=>26}, {:first=>27, :last=>28}, {:first=>29, :last=>30}, {:first=>31, :last=>32}, {:first=>33, :last=>34}, {:first=>35, :last=>36}, {:first=>37, :last=>38}, {:first=>39, :last=>40}, {:first=>41, :last=>42}, {:first=>43, :last=>44}, {:first=>45, :last=>46}, {:first=>47, :last=>48}, {:first=>49, :last=>50}, {:first=>51, :last=>52}, {:first=>53, :last=>54}, {:first=>55, :last=>56}, {:first=>57, :last=>58}, {:first=>59, :last=>60}, {:first=>61, :last=>62}, {:first=>63, :last=>64}, {:first=>65, :last=>66}, {:first=>67, :last=>68}, {:first=>69, :last=>70}, {:first=>71, :last=>72}, {:first=>73, :last=>74}, {:first=>75, :last=>76}, {:first=>77, :last=>78}, {:first=>79, :last=>80}, {:first=>81, :last=>82}, {:first=>83, :last=>84}, {:first=>85, :last=>86}, {:first=>87, :last=>88}, {:first=>89, :last=>90}, {:first=>91, :last=>92}, {:first=>93, :last=>94}, {:first=>95, :last=>96}, {:first=>97, :last=>98}, {:first=>99, :last=>99}]

Now at this point I'm not sure what that function is doing that is assigned to $distances. You might want to provide the code for that or give some more detail on what your are attempting to accomplish.

You are right, i chaged it and now the problem is a different. Ill explain above
Updated my response, also I noticed you had another to_a in there right before map. You shouldn't need that.
Actually, each returns self by convention, but you are right that each_slice returns nil.
So does the map-function only return the first value, as array

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