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Hi everyone again :)

Bit of a weird problem, but is there any way of counting how many keys are stored within a multimap?

Say for example I have the keys A, B, C and D. Each of these keys have say 100 values for each, so there should be 100 instances of A, 100 of B and so on. I know how to count how many pairs there are for the keys, but is there a way of counting how many unique keys there are in the multimap (in this case you should get 4)?

Many thanks in advance :)