How to determine last object in each loop?

Question

In your typical each loop in Rails, how do I determine the last object, because I want to do something different to it than the rest of the objects.

<% @stuff.each do |thing| %>

<% end %>

score 66 · Answer 1 · answered Feb 13 '13 at 09:12

66

@stuff.each do |s|
  ...normal stuff...
  if s == @stuff.last
    ...special stuff...
  end
end

answered Feb 13 '13 at 09:12

abject_error

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2

this is the best answer... could be a touch better if you'd like to 1-line it. `s == @stuff.last ? 'thing for last' : 'things for the rest'` – Dudo Oct 01 '13 at 01:34
16

warning: this won't work if @stuff elements aren't unique. ie "a = [1,1];a.map{|v| v == a.last}" returns [true,true]. in case of integers there's no way to determine if it's really last element. if using other objects, you can use equal? (http://stackoverflow.com/questions/7156955/whats-the-difference-between-equal-eql-and) – Pavel K. Dec 03 '13 at 15:11
this will also not work if @stuff is an `io` or some other `Enumerator` and not an array (e.g. `io`). One can use `Enumerator#next` instead like https://stackoverflow.com/a/59556778/520567 – akostadinov Jan 01 '23 at 22:56

score 33 · Answer 2 · edited Jun 13 '12 at 18:13

33

Interesting question. Use an each_with_index.

len = @stuff.length

@stuff.each_with_index do |x, index|
 # should be index + 1       
 if index+1 == len
 # do something
  end
end

edited Jun 13 '12 at 18:13

Jakub Kuchar

1,665
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answered May 30 '09 at 06:43

A.Ali

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I find `if index == len + 1` more aesthetic. – Benjamin J. Benoudis Apr 12 '15 at 04:11
isn't it suppose to be @stuff.each_with_index do |index, x|? (first the object and then the index) – Feb 01 '16 at 10:50
8

@BenjaminBenoudis that would be `if index == len - 1` – andreofthecape Oct 28 '16 at 06:45

score 8 · Answer 3 · answered Feb 13 '13 at 09:04

8

<% @stuff[0...-1].each do |thing| %>
  <%= thing %>
<% end %>
<%= @stuff.last %>

answered Feb 13 '13 at 09:04

jackpipe

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Much nicer than checking every iteration if we're at the end! Although I think you have one too many `.`'s? – Matt Aug 31 '16 at 14:06
Thanks! Actually it's a little confusing, since `-1` in a range stands for "the last element", so actually `stuff[0..-1] == stuff`. We need to use the `...` form of range which omits the last element. – jackpipe Jan 12 '17 at 06:48
I see! You should add that to the answer to make it a bit clearer and save stupid questions like mine ;) – Matt Jan 12 '17 at 14:48

score 2 · Answer 4 · answered May 30 '09 at 06:44

2

A somewhat naive way to handle it, but:

<% @stuff.each_with_index do |thing, i| %>
  <% if (i + 1) == @stuff.length %>
    ...
  <% else %>
    ...
  <% end %>
<% end %>

answered May 30 '09 at 06:44

apostlion

720
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score 2 · Answer 5 · answered Jun 01 '09 at 20:37

2

A more lispy alternative is to be to use

@stuff[1..-1].each do |thing|

end
@stuff[-1].do_something_else

answered Jun 01 '09 at 20:37

Sam

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score 0 · Answer 6 · answered Sep 04 '22 at 15:55

Surprised this is not listed as an answer, but to my this is the cleanest way to do it. By starting the index at 1, you can remove the math of making the index and size match up.

@stuff = [:first, :second, :last]

@stuff.each.with_index(1) do |item, index|
  if index == @stuff.size
    # last item
  else
    # other items
  end
end

also the added benefit here is that you can use this on the .map as well.

How to determine last object in each loop?

6 Answers6