help counting items unique to a day/customer combination

Help please.
I need to identify the number of occasions on which a product type is bought by a customer in isolation from other product types. I have attached a sample to illustrate. The actual data is more complex and is actually medical data concerning issue of oral or IV drugs. There are many thousands of records.

To clarify, in the example, there was only one occasion when Bread was bought on its own by a particular customer on a particular day. The way the data is presented, 'Bread' could be listed before 'Milk' or, as with 'Steve' on the 2/4, it could be in the middle of a series of 'Milk' purchases.

I can sort by date/name/type, but I cant work out a formula to resolve the count.

Thanks in advance for any help.

Hmm... I suspect there's no really nice efficient way of doing this using formulae, one approach might be to use some "helpers" to ease the expensive calc burden... eg:

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If then say B19 contains Milk and B20 Bread then:

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would return 3 & 1 ... if you changed C3 to say Milk from Bread the result for C19 would become 4

Is that something you can work with ?