Question

Rails has a nice function, ordinalize, which converts an integer to a friendly string representation. Namely 1 becomes 1st, 2 becomes 2nd, and so on. My question is how might one implement the inverse feature?

To be more general I’d like to handle both of the following cases:

>> s = 'First' >> s.integerize => 1 >> s = 1st >> s.integerize => 1 

I am looking for an smart way to do this as opposed to a giant lookup table or just hacking off the last two characters. Any ideas would be appreciated.

Answer 1

to_i does essentially 1/2 of that:

'72nd'.to_i => 72 

It doesn’t check validity, but if you need to fail on bad input like ’72x’, you can just re-ordinalize and compare to the original input string.

For parsing ordinal words, Wikipedia seems impressively helpful.