Question

i want to following select tag

<select>
<option value=10> 10% </option>
<option value=20> 20% </option>
<option value=30> 30% </option>
</select>

using

 ((0..10).to_a.collect {|r| ["#{r*10} %", r*10] })

will give structure like

[["0 %", 0], ["10 %", 10], ["20 %", 20], ["30 %", 30]]

i wonder if this structure can be converted to something like this

[#<ratio id: 10, name: "10%">, #<id: 20, name:"20%">]

how to convert first structure to second strcuture

so i could use

options_from_collection_for_select(@arr,"id","name")

to populate the select_tag
or

is there any better way to do the same?

comments please.

Answer 1

You can try to use OpenStruct for this.

An OpenStruct is a data structure, similar to a Hash, that allows the
definition of arbitrary attributes with their accompanying values.
This is accomplished by using Ruby’s metaprogramming to define methods
on the class itself.

require 'ostruct'
(0..10).map { |i| OpenStruct.new(:id => i*10, :name => "#{i*10}%") }
# => [#<OpenStruct id=0, name="0%">, #<OpenStruct id=10, name="10%">, ...

But if you need a real class, not anonymous class like OpenStruct, then just create this class instances inside the collect/map method:

class Ratio
    attr_reader :id, :name
    def initialize(id, name)
        @id = id; @name = name
    end
end
(0..10).map { |i| ratio = i*10; Ratio.new(ratio, "#{ratio}%") }
# => [#<Ratio: @id=0, @name="0%">, #<Ratio: @id=10, @name="10%">, ...

---

Maybe I misunderstood you a bit and you want to create this structure not from range, but from array [["0 %", 0], ["10 %", 10], ["20 %", 20], ["30 %", 30]] then the code is similar:

require 'ostruct'
arr = [["0 %", 0], ["10 %", 10], ["20 %", 20], ["30 %", 30]]
p arr.map { |name, id| OpenStruct.new(:id => id, :name => name) }
# => [#<OpenStruct id=0, name="0 %">, #<OpenStruct id=10, name="10 %">, #<OpenStruct id=20, name="20 %">, #<OpenStruct id=30, name="30 %">]

---

UPDATE
I found one corner case in usage of OpenStruct (looks like this is the case for Ruby 1.8.7 only): OpenStruct#id will return object_id for id instead of field value:

ruby-1.8.7-p352 > o = OpenStruct.new :id => 10
 => #<OpenStruct id=10> 
ruby-1.8.7-p352 > o.id
(irb):4: warning: Object#id will be deprecated; use Object#object_id
 => 70021843187380 

There are two workarounds:

# 1. redefine OpenStruct#id method: 
OpenStruct.__send__(:define_method, :id) { @table[:id] }

# 2. dont use 'id' as a value and use any other value:
require 'ostruct'
(0..10).map { |i| OpenStruct.new(:value => i*10, :name => "#{i*10}%") } # 'value' instead of 'id'

...
options_from_collection_for_select(@arr, 'value', 'name')

I recommend you to use second approach.