Tell the end of a .each loop in ruby

问题

If i have a loop such as

users.each do |u|
  #some code
end

Where users is a hash of multiple users. What's the easiest conditional logic to see if you are on the last user in the users hash and only want to execute specific code for that last user so something like

users.each do |u|
  #code for everyone
  #conditional code for last user
    #code for the last user
  end
end

回答1:

users.each_with_index do |u, index|
  # some code
  if index == users.size - 1
    # code for the last user
  end
end

回答2:

If it's an either/or situation, where you're applying some code to all but the last user and then some unique code to only the last user, one of the other solutions might be more appropriate.

However, you seem to be running the same code for all users, and some additional code for the last user. If that's the case, this seems more correct, and more clearly states your intent:

users.each do |u|
  #code for everyone
end

users.last.do_stuff() # code for last user

回答3:

I think a best approach is:

users.each do |u|
  #code for everyone
  if u.equal?(users.last)
    #code for the last user
  end
end

回答4:

Did you tried each_with_index?

users.each_with_index do |u, i|
  if users.size-1 == i
     #code for last items
  end
end

回答5:

h = { :a => :aa, :b => :bb }
h.each_with_index do |(k,v), i|
  puts ' Put last element logic here' if i == h.size - 1
end

回答6:

Sometimes I find it better to separate the logic to two parts, one for all users and one for the last one. So I would do something like this:

users[0...-1].each do |user|
  method_for_all_users user
end

method_for_all_users users.last
method_for_last_user users.last

回答7:

You can use @meager's approach also for an either/or situation, where you're applying some code to all but the last user and then some unique code to only the last user.

users[0..-2].each do |u|
  #code for everyone except the last one, if the array size is 1 it gets never executed
end

users.last.do_stuff() # code for last user

This way you don't need a conditional!

回答8:

Another solution is to rescue from StopIteration:

user_list = users.each

begin
  while true do
    user = user_list.next
    user.do_something
  end
rescue StopIteration
  user.do_something
end

回答9:

There are no last method for hash for some versions of ruby

h = { :a => :aa, :b => :bb }
last_key = h.keys.last
h.each do |k,v|
    puts "Put last key #{k} and last value #{v}" if last_key == k
end

来源：https://stackoverflow.com/questions/4000713/tell-the-end-of-a-each-loop-in-ruby

标签

ruby-on-rails

ruby

loops

each