set expression to count customer who only purchasing selective products at one product group without purchasing other products at that group

[coloful_architect]

hi gurus,

so I have a data structure like this 

product group, product, customer, units ,sales

let 's say one of product groups is beverage, so product would be soda, juice , etc  but we have other product group like 

bread, diary .... 

now I want to know the count of customers who have only purchased product 'Juice' under product group of beverage without purchasing any other beverage products across the board ....that means,  the count of those customers who have only purchased Juice but may also purchased bread products or diary products.....

so far I seem to be able to  get the customer count that only purchasing Juice without purchasing any other products at all... like 

Count({$<[Product Group]={'beverage'}, [Customer Full Name] ={"=Count( Distinct [Product Group])=1"}>} [Customer ])

but do not get correct numbers by keeping the exclusion only at the level of product group of beverage 

any suggestions?

Thanks 

[Anil_Babu_Samineni]

Perhaps this?

Count({$<[Product Group]=E({$<[Product Group]-={'beverage'}>} [Product Group]), [Customer Full Name] ={"=Count( Distinct [Product Group])=1"}>} [Customer ])