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 may be omitted if order is not significant

uniq -c 

or

echo "$list" | uniq -c

if the source list is a variable