simple efficiency question: repeated iteration in the view

rubyonrails-talk
1

Let's say I get a list of all places from the database in the controller:   @places=Place.find(:all, :order=>"category_id")

And in the view I want to list them under category headings

Now let's imagine categories is a hash like this {0=>'Museum',1=>'Gallery',2=>'Historic House'}

The only way I can think of doing it is by traversing the whole list for every category, ie:

<% categories.each do | key,value | %> <%= value %><br /> <% @places.each do | place | %> <%= place.title if place.category_id==key %> <% end %> <% end %>

Is there a better way of doing this that doesn't involve traversing the entire array so many times?

Thanks.

2

two ideas are:

1) execute 1 find for each category in the controller and pass the results to the view as separate collections. Can't be sure of the relative perfomance though.

2) use a CASE or if/else if block in the view to presort the places into Collections on singlepass then render each collection under the apporopriate category heading. This should be faster then traversing the array multiple times but may clutter up you view logic

Brian

3

use #group_by. It takes your array of @places and creates a structure like this:

{0 => [<place>, <place>], 1 => [<place>], ...}

@places=Place.find(:all, :order=>"category_id") @category_places = @places.group_by { |p| p.category_id } @categories = {0=>'Museum',1=>'Gallery',2=>'Historic House'}

@categories.each do |category_id, category|   puts category   @category_places[category_id].each do |place|     puts place   end end

4

Rick - brilliant. Thanks.