ruby number to human-readable string conversion -

I should have a list with id for each list item #one , #two etc. Is this the most effective way or do I remember a built-in Ruby function here?

  -num_array = ["one", "two", "three", "four", "five", "six", "seven"] -file [: primary_level] .each_with_index Do Primary_item, idx | % Li {: id = & gt; "# {Num_array [idx]}"}  

Manly converts digits into words is.