Rails, collection_select - remembering values with :selected after form submitted

(Using Rails 2.3.5 on an internal work server with no choice of versions, and I'm pretty new)

I'm building a search form where I need to provide a list of directories to a user so they can select which one(s) to search against. I'm trying to figure out how to get the selected values of a collection_select to remain after the form is submitted.

Say the user selected 3 directories from the collection_select, the id's of those directories would look like this in the params:

directory: !map:HashWithIndifferentAccess 
  id: 
  - "2"
  - "4"
  - "6"

I know that you can manually specify multiple selected items:

<%= collection_select :directory, :id, @directories, :id, :name,
                 {:selected => [2,4,6]}, {:size => 5, :multiple => true} %>

I've also played around a bit and was able to us "to_i" against a single value in the params hash:

<%= collection_select :directory, :id, @directories, :id, :name,
                 {:selected => params[:directory][:id][0].to_i}, {:size => 5, :multiple => true} 开发者_如何学Go%>

What I can't figure out is how to use all of the values of the :directory params at the same time so what the user selected remains after the form is submitted. Thanks for any help.

---

I'm not precisely sure what you're asking, but if you're trying to get the array of strings in params[:directory][:id] as an array of integers, all you need is

params[:directory][:id].map{|id|id.to_i}