How to join integers with a comma without haveing a trailing comma at the end

If I do this:

users.each do |u|
   str += u.id.to_s + ','
end

I will end up with:

1,3,234,234,

Is there a style of looping that won't leave the trailing ',' at the end? I know I can chomp it off after the loop, but was looking fo开发者_如何学运维r a way to do it w/o having to do that.

Or even shorter:

users.map(&:id).join ','

users.map { |u| u.id.to_s }.join ','

And actually, #join will do the #to_s for you, so on second thought:

users.map(&:id).join ','