gistfile1.rb

require 'benchmark'

size = 1048576

data = []
genders = ['male', 'female']
size.times do
  data << [genders[rand * 2]]
end

a = 0b00
data.each_with_index do |row, index|
  if row.first == 'male'
    a += 1
  end
end

positions = []
puts Benchmark.measure {
  0.upto(size) do |position|
    positions << position if a[position] == 1
  end 
}