Question

I’m doing the following:

def createDTable
  dTable = Array.new
  cTable.each_index do |i|
    dTable[cTable[i]] = i
  end
end

Is there any way this (very simple) code can be optimized, especially for large cTable and sparse dTable ?

Answer 1

I was curious so I benchmarked it. (http://ruby-doc.org/stdlib-1.9.3/libdoc/benchmark/rdoc/Benchmark.html)

I generated random numbers for the C table. Basically it was better speed-wise to use an Array if the values were within the length of the array, and better to use a Hash when they were much larger.

I tried it with 5 different combinations:

randoms to 10,000, array size 100,000 => Array
randoms to 100,000, Array size 10,000 => Hash
randoms to 100,000, array size 100,000 => Array
randoms to 1,000,000, Array size 100,000 => Array
randoms to 10,000,000, Array size 100,000 => Hash

So anyway, here’s my alternate code, but you may be just fine.

def create_d_hash(c_table)
  d_hash = {}
  c_table.each_with_index do |value, index|
    d_hash[value] = index
  end
  d_hash
end