CODEWITHSUNDEEP
rubysyntax
Dan Rosenstark
Dan Rosenstark

Reputation: 69757

Automatic counter in Ruby for each?

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?

Note: I don't know if blahs is an array or a hash, but having to do blahs[i] wouldn't make it much sexier. Also I'd like to know how to write i++ in Ruby.

Technically, Matt's and Squeegy's answer came in first, but I'm giving best answer to paradoja so spread around the points a bit on SO. Also his answer had the note about versions, which is still relevant (as long as my Ubuntu 8.04 is using Ruby 1.8.6).

Should've used puts "#{i} #{blah}" which is a lot more succinct.

Upvotes: 140

Views: 80506

Answers (8)

Ilyas karim
Ilyas karim

Reputation: 4812

If you want to get index of ruby for each, then you can use

.each_with_index

Here is an example to show how .each_with_index works:

range = ('a'..'z').to_a
length = range.length - 1
range.each_with_index do |letter, index|
    print letter + " "
    if index == length
        puts "You are at last item"
    end
end

This will print:

a b c d e f g h i j k l m n o p q r s t u v w x y z You are at last item

Upvotes: 3

Roy Pardee
Roy Pardee

Reputation: 196

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

Upvotes: 1

pope
pope

Reputation: 629

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.

Upvotes: 4

Matt Rogish
Matt Rogish

Reputation: 24873

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}

Upvotes: 11

paradoja
paradoja

Reputation: 3090

As people have said, you can use 

each_with_index

but if you want indices with an iterator different to "each" (for example, if you want to map with an index or something like that) you can concatenate enumerators with the each_with_index method, or simply use with_index:

blahs.each_with_index.map { |blah, index| something(blah, index)}

blahs.map.with_index { |blah, index| something(blah, index) }

This is something you can do from ruby 1.8.7 and 1.9.

Upvotes: 196

George
George

Reputation: 3126

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

Upvotes: 6

Andrew Grimm
Andrew Grimm

Reputation: 81520

The enumerating enumerable series is pretty nice.

Upvotes: 2

Alex Wayne
Alex Wayne

Reputation: 187034

[: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.

Upvotes: 56

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