Best way to simulate “group by” from bash?

Question

Suppose you have a file that contains IP addresses, one address in each line:

10.0.10.1
10.0.10.1
10.0.10.3
10.0.10.2
10.0.10.1

You need a

Answer 1

sort ip_addresses | uniq -c

This will print the count first, but other than that it should be exactly what you want.