finding keys in a table

[Jelle Huisman <jelle@...>]

Hello,

I need a frequency list of all characters in a text file and I try to 
use a table for this but I'm not totally sure if this is the best way to 
solve my problem. Anyway I setup a table "count" with the characters as 
key and a counter as value. When I iterate over my data I want to:
(1) lookup if the current character already exists as a key in the table.
(2a) If it does exist I increment the value for key currentchar with 1
(2b) else I add a new entry: currentchar=1
(3) Later I sort the table and print my freq.list.

The two questions I have are: is this the best/most efficient/fastest 
way to do this?
Second: How do I check if a key exists? (I don't think I can use an 
inverted table because I'll end up with duplicate keys, or not?)

Thanks for some advice,

Jelle