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Extracting All Subarray Indices From A Multi-dimensional Array

04.22.2006

| 4054 views |

        Note the use of Array#fetch to define return values for missing indices!
Example: ar = []; x = ar.fetch(5, [])  returns an empty array for non-existing index 5.


class Array

   def subar_indices(ar=[], temp=[])
      temp = temp.dup
      self.each_with_index { |item, index| 
         if item.class == Array
            temp << index
            ar << temp
            ar = item.subar_indices(ar, temp)
         end
      }
      ar.uniq
   end


   def extract_subar_indices
      subarray_indices = self.subar_indices  # subarray_indices is a two-dimensional array
      # puts subarray_indices.inspect
      
      return subarray_indices if subarray_indices.empty?

      first_subar = subarray_indices.shift   # the first subarray contains all two-dimensional subarray indices                

      subarray_indices.each do |subar|
         subar_size = subar.size
         str = ""
         count = -1
         (subar_size - 1).times { count += 1; str << ".fetch(subar[#{count}], [])" }
         str << ".fetch(subar[#{count + 1}], {}"
         str = "self" << str
         if eval(str).class == Hash then subar.shift; redo end
      end

      first_subar.reverse.each do |item| subarray_indices.unshift([item]) end
      subarray_indices
   end

end


array = [1, 2, [3, 4, [5, 6]], 7, 8, [9]]

indices = array.extract_subar_indices

puts indices.inspect  # [[2], [5], [2, 2]]

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Comments

Snippets Manager replied on Sun, 2006/01/29 - 5:07pm

Just for completion, here's a way to do it:



indices = array.extract_subar_indices  # for array in main snippet above

indices = indices.sort_by { |subar| subar.size }.reverse

indices.each do |subar_index|
   subar_index_size = subar_index.size
   str = ""
   (subar_index_size).times { |x| str << "[subar_index[#{x}]]" }
   str = "array" << str
   eval(str) << "new item"   # eval(str) is subarray

   if eval(str).include?(3) && eval(str).size > 2
      eval(str).reverse!
      eval(str).unshift("unshifted item")
      eval(str).sort_by { |item| item.size }
      eval(str).replace(["replaced subarray"])
   end

end


puts array.inspect   #  [1, 2 ["replaced subarray], 7, 8, [9, "new item]]

Snippets Manager replied on Sun, 2006/01/29 - 5:07pm

Well, obviously, it's a way to add items to any subarray without any prior knowledge of subarray indices (... or Subarray#replace, sort, reverse, ...).