Exercise: improve the csv reader
Instead of an array create a hash in which the key is
the fname and the value is the hash reference.
To get the phone of 'Foo' we could write:
- First you can assume fname values are unique.
- Then improve it by checking if the fname is indeed unique and warn if not.
- Further improve it by removing the fname from the internal hashes.
- Further improve by passing the name of the key field (currently fname) as a parameter.
- Bonus: try to deal with the case when there are duplicate values for the key field without just giving an error message.