What's the point of a hash table?

Question

I don\'t have experience with hash tables outside of arrays/dictionaries in dynamic languages, so I recently found out that internally they\'re implemented by making a hash

Answer 1

The main advantage of using a hash for the purpose of finding items in the table, as opposed to using the original key of the key-value pair (which BTW, it typically stored in the table as well, since the hash is not reversible), is that..

...it allows mapping the whole namespace of the [original] keys to the relatively small namespace of the hash values, allowing the hash-table to provide O(1) performance for retrieving items.

This O(1) performance gets a bit eroded when considering the extra time to dealing with collisions and such, but on the whole the hash table is very fast for storing and retrieving items, as opposed to a system based solely on the [original] key value, which would then typically be O(log N), with for example a binary tree (although such tree is more efficient, space-wise)