How to display an array of array

Question

I have a some code in my controller:

def index
 @tasks = Task.paginate(page: params[:page], per_page: 12 )    
 @tasks_row = task_to_rows(@tasks)

 respond_to do |format|
  format.html # index.html.erb
  format.json { render json: @tasks }
 end
end

task_to_rows:

def task_to_rows(tasks)
  item_at_row = 0
  task_row = Array.new
  for i in (0..tasks.length)
    item_at_row += 1
    if item_at_row == 1
      temp_arr = Array.new
      temp_arr << tasks[i]
      task_row << temp_arr
    elsif item_at_row <= 3
      temp_arr << tasks[i]
      task_row << temp_arr
    end
    item_at_row = 0 if item_at_row == 3
  end

  return task_row
end

Method is needed to that each element of the array was an array of three elements. And to be able to show information like this: https://www.evernote.com/shard/s8/sh/5dee1bbd-af05-4432-9e24-586de98f4452/a8229d8d3fd0bb222a76a927a70ee507

In view I have:

<% @tasks_row.each do |task3| %>
  <h3>Row</h3>
  <% task3.each do |task| %>
    <%= task.name %>
  <% end -%>
<% end -%>

But Rails display a error:

undefined method `name' for nil:NilClass

If debug, then all works fine and shows.

UPDATE: In the final version I just need to display the data in this format:

<div class="row>
  <div class="span3">Some data</div>
  <div class="span3">Some data</div>
  <div class="span3">Some data</div>
</div>
<div class="row">
  <div class="span3">Some data</div>
  <div class="span3">Some data</div>
  <div class="span3">Some data</div>
</div>
.........

hm, what does <% @tasks_row.each do |task3| %> <%= task3 %> <% end -%> return or what does the final array structure look like?? — shayonj
– shayonj, Commented Mar 31, 2013 at 15:21
<% @tasks_row.each do |task3| %> <h3>Row</h3> <%= task3 %> <h3>end Row</h3> <% end -%> it return evernote.com/shard/s8/sh/7a79cae1-0604-4047-9019-d4ea35d527c3/… — Ivo Dimitrov
– Ivo Dimitrov, Commented Mar 31, 2013 at 15:25
are you getting data in @tasks when you are not in debug mode? — goyalankit
– goyalankit, Commented Mar 31, 2013 at 15:29

jvnill · Accepted Answer · 2013-03-31 15:25:16Z

1

If I understand task_to_rows correctly, you want the array grouped by 3 right? In that case, I suggest you use each_slice(3) instead. The method you added is error prone and may result to some nil elements which causes the error. Remember that tasks[i] can become nil if i is greater than or equal to the length of your array. This is most probably where the error comes in since you are using tasks.length. So you have 2 choices.

Choice 1

Change

for i in (0..tasks.length)

to

for i in (0..(tasks.length - 1))

Choice 2

Use each_slice(3)

@tasks_row = @tasks.each_slice(3)

answered Mar 31, 2013 at 15:25

jvnill

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