Group array of strings by first common characters

group_by_common_chars.rb

def group_by_common_chars(strings_array)  
  max_length = strings_array.max_by(&:length).length
  char_grouped_hash = (0..max_length).each_with_object({}) do |index, hash|
    hash.merge!(strings_array.group_by { |string| string[0..index] }.select{|k, v| k.length == index + 1})
  end

  index = 0
  result_hash = {}
  char_grouped_hash.each do |key, values_array|
    index += 1
    result_hash[key] = values_array.sort
    next if 1 == index

    values_array.each do |value|
      keys = result_hash.select{ |k, v| v.include?(value) && k != key }.keys
      if 1 == values_array.size && keys.present?
        if result_hash[keys.first].size == 1
          result_hash.delete(keys.first)
        else
          result_hash.delete(key)
        end
      else
        keys.each do |ke|
          result_hash[ke].delete(value)
        end
      end
    end
  end

  result_hash.reject!{|k, value| value.size.zero?}
end