How can I use Array#delete while iterating over the array?

Question

I have an array that I want to iterate over and delete some of the elements. This doesn't work:

a = [1, 2, 3, 4, 5]
a.each do |x|
  next if x < 3
  a.delete x
  # do something with x
end
a #=> [1, 2, 4]

I want a to be [1, 2]. How can I get around this?

Answer 1

a.delete_if { |x| x >= 3 }

See method documentation here

Update:

You can handle x in the block:

a.delete_if do |element|
  if element >= 3
    do_something_with(element)
    true # Make sure the if statement returns true, so it gets marked for deletion
  end
end

Answer 2

I asked this question not long ago.

http://stackoverflow.com/questions/2933366/deleting-while-iterating-in-ruby

It's not working because Ruby exits the .each loop when attempting to delete something. If you simply want to delete things from the array, delete_if will work, but if you want more control, the solution I have in that thread works, though it's kind of ugly.

Answer 3

You don't have to delete from the array, you can filter it so:

a = [1, 2, 3, 4, 5]

b = a.select {|x| x < 3}

puts b.inspect # => [1,2]

b.each {|i| puts i} # do something to each here