How do I construct a f.collection_select menu with custom options (not from a database)?

Question

I'm using Rails 4.2.3. I would like to construct a select menu in my form, in which both the name and value are the same option and I would like to construct the options from an array. I tried this

<%= f.collection_select :unit, options_for_select([['km'], ['mi']]) %>

but got the error

wrong number of arguments (given 2, expected 4..6)

How do I construct the above properly? I would like there to be an additional option with a blank value that reads "Select Unit".

Thanks, - Dave

Answer 1

You should use the select method instead of the collection_select

<%= f.select :unit, [['km', 'km'], ['mi', 'mi']] %>