counting ip addresses

I am trying to write a routine to provide counts from a list of IP
addresses that are sorted.

example:

2.3.4.5
2.3.4.5
2.3.4.5
10.20.20.40
10.20.20.40

report would like this 2.3.4.5 - sum 3
10.20.20.40 - sum 2

thanks

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