Question

I am trying to understand this code snippet:

while row = input.gets
  row.strip!
  next if row.empty?

  valuesplit = row.split("---")
  a, b = valuesplit[1..2]
  unless a == b
    $hash1[a] ||= {} <--------------What is this line doing?  How is the whole loop
    $hash1[a][b] = true               being traversed?

    if $hash1[b] && $hash1[b][a] <-----Can you please describe this if() loop
      $hash2[a] ||= []
      $hash2[a] << b
      $hash2[b] ||= []
      $hash2[b] << a
    end
  end
end

NOTE: $hash1 = {}
$hash2 = {}

Thanks!

UPDATE

Input:

junkdata1 value1 value2
junkdata2 value3 value4
junkdata3 value5 value6

and so on.

Updated the code lines with comments too.

Answer 1

# loops by reading in every line of the input
# (input can be a file or another I/O object)
# every line is stored successively in a variable
# called "row"
while row = input.gets

  # removes leading and trailing whitespace from
  # the string that is stored in the "row" variable
  row.strip! 

  # if the string is empty, continue to the next
  # line (go back to beginning of loop)
  next if row.empty? 

  # split the string into an array of substrings
  # based on the "---" delimiter
  valuesplit = row.split("---") 

  # assign the second substring in the valuesplit
  # array to a variable called a, and the third to
  # a variable called b
  a, b = valuesplit[1..2] 

  # if a and b are different
  unless a == b

    # initialize the hash1 dictionary's a entry
    # to an empty sub-dictionary if it is null
    $hash1[a] ||= {} 

    # in the hash1 dictionary, set a's entry
    # to a dictionary that has b as the entry
    # and true as the value
    $hash1[a][b] = true

    # if the value for the b entry in the hash1
    # dictionary is true (not false or null) AND the value for a's
    # entry of the dictionary found at the b
    # entry of the hash1 dictionary is true
    if $hash1[b] && $hash1[b][a] 

      # initialize the hash2 dictionary's a entry
      # to an empty arraylist if it null or false
      $hash2[a] ||= [] 

      # add b to this arraylist
      $hash2[a] << b

      # initialize the hash2 dictionary's b entry
      # to an empty arraylist if it null or false
      $hash2[b] ||= []

      # add a to this arraylist
      $hash2[b] << a 
    end # end of the if $hash1[b]... statement
  end # end of the unless a == b statement
end # end of the gets loop