Exclude option from collection.map in Ruby on Rails?

Question

I have a line like this:

<%= f.input :state_id, :input_html => {:value => (policy_address.state.name rescue nil)}, :required => true, :collection => states.map {|s| [ s.name, s.id] }, :include_blank => 'Please select'%>

I want to exclude a value from the states.map collection. I thought that this would work but it doesn't:

<%= f.input :state_id, :input_html => {:value => (policy_address.state.name rescue nil)}, :required => true, :collection => states.map {|s| [ s.name, s.id] unless s.name == "excluded_state" }, :include_blank => 'Please select'%>

I put in unless s.name == "excluded_state, but, again, it's not working:

What am I doing wrong?

Answer 1

map doesn't allow to skip values. You have to reject unwanted elements first.

states.reject { |s| s.name == "excluded_state" }.map { |s| [s.name, s.id] }

Another (dirtier) solution is to return nil for excluded elements and use Array#compact on the resulting array to remove those nil elements:

states.map { |s| s.name == "excluded_state" ? nil : [s.name, s.id] }.compact

Answer 2

Eureka's answer is good but here is just a brief explanation to clarify what's going on.

map returns a new array with the results of running block once for every element in the array. When you write [s.name, s.id] unless s.name == "excluded_state" this causes the block to return nil when s.name == "excluded_state" i.e. the result would be something like

[["NY", 1], nil, ["CA", 2]]

So you could use reject to remove the unwanted state first, or you could just use compact¹ to remove the nil entry on the result of your map as you originally wrote it.

---

1. Array#compact returns a copy of the array with all nil elements removed.