Automatic counter in Ruby for each?

Question

I want to use a for-each and a counter:

i=0
for blah in blahs
    puts i.to_s + \" \" + blah
    i+=1
end

Is there a better way to do it?

Answer 1

Yes, it's collection.each to do loops, and then each_with_index to get the index.

You probably ought to read a Ruby book because this is fundamental Ruby and if you don't know it, you're going to be in big trouble (try: http://poignantguide.net/ruby/).

Taken from the Ruby source code:

 hash = Hash.new
 %w(cat dog wombat).each_with_index {|item, index|
   hash[item] = index
 }
 hash   #=> {"cat"=>0, "wombat"=>2, "dog"=>1}

Answer 2

The enumerating enumerable series is pretty nice.

Answer 3

[:a, :b, :c].each_with_index do |item, i|
  puts "index: #{i}, item: #{item}"
end

You can't do this with for. I usually like the more declarative call to each personally anyway. Partly because its easy to transition to other forms when you hits the limit of the for syntax.

Answer 4

If you don't have the new version of each_with_index, you can use the zip method to pair indexes with elements:

blahs = %w{one two three four five}
puts (1..blahs.length).zip(blahs).map{|pair|'%s %s' % pair}

which produces:

1 one
2 two
3 three
4 four
5 five

Answer 5

As to your question about doing i++, well, you cannot do that in Ruby. The i += 1 statement you had is exactly how you're supposed to do it.

Answer 6

If blahs is a class that mixes in Enumerable, you should be able to do this:

blahs.each_with_index do |blah, i|
  puts("#{i} #{blah}")
end