CODEWITHSUNDEEP
ruby-on-railsruby
Trs MTV
Trs MTV

Reputation: 67

Next iteration in `each` loop

I have a collection:

@monday = HomeTask.where(:class_room => current_user.class_room, :day => 'Понеділок').order(created_at: :desc)

The @monday variable contains data from the database. In view, I show all dates from the collection:

<% @monday.each_with_index do |mnd, i| %>
  <% if mnd.data == mnd.data[i + 1] %>
    <%= link_to 'nice' %>
  <% else %>
    <%= link_to 'ohhh...' %>
  <% end %>
<% end %>

Within if body, I want to refer to the next element. But it does not work. In C++, to refer to the next element in the first iteration, it would be coded like this:

if(array[i] == array[i+1])

How do I use each in Ruby?

Upvotes: 1

Views: 374

Answers (3)

ray
ray

Reputation: 5552

What if you could go with following changes,

-  <% if mnd.data == mnd.data[i + 1] %>
+  <% if @monday[i+1] != nil && mnd.data == @monday[i+1].data %>

Or simply,

-  <% if mnd.data == mnd.data[i + 1] %>
+  <% if mnd.data == @monday[i+1].try(:data) %>

Upvotes: 0

Cary Swoveland
Cary Swoveland

Reputation: 110665

arr = [1,2,3,4,5,6,7,8]

enum = arr.to_enum
  #=> #<Enumerator: [1, 2, 3, 4, 5, 6, 7, 8]:each>    
loop { puts "%d : %d" % [enum.next, enum.peek] }
1 : 2
2 : 3
3 : 4
4 : 5
5 : 6
6 : 7
7 : 8

See Kernel#to_enum1, Kernel#loop, Enumerator#next and Enumerator#peek. peek raises a StopIteration exception when it is executed after the last element of arr has been generated. loop handles that exception by breaking out of the loop.

1. As to why this Kernel instance method is documented as an Object instance method, please see the second paragraph at the docs for Object.

Upvotes: 4

Shira Elitzur
Shira Elitzur

Reputation: 441

If you want to iterate an array and have access to more than one item in each iteration you can use each_cons

arr = [1,2,3,4,5,6,7,8]
arr.each_cons(2){|a,b| 
   puts "#{a} : #{b}"
}
# 1 : 2
# 2 : 3
# 3 : 4
# 4 : 5
# 5 : 6
# 6 : 7
# 7 : 8

Using each_cons you can easily compare two (or more) consecutive items of an array.

Upvotes: 6

Related Questions