Summarize but only first value

[weasel_girl]

I'm trying to summarize some data, but only want to keep the first instance of one of the categories. 

Data example 'Shops' here: 

Product	Shop type	Shop category
Bread rolls	Supermarket	Big store
Bread rolls	Bakery	Little store
Bread rolls	Freezer shop	Little store
Vodka	Supermarket	Big store
Paracetamol	Supermarket	Big store
Paracetamol	Pharmacy	Little store
Tomatoes	Farmer	Little store

Shop category is a calculated column based on Shop type. 

I'd want the summarized output to be:

Product	Main category
Bread rolls	Big store
Vodka	Big store
Paracetamol	Big store
Tomatoes	Little store

Is there a way of doing this in SUMMARIZE? 

At the moment my summarize command is:

ShopSummary = SUMMARIZE('Shops','Shops'[Product],'Shops'[Main Category]) 

but (understandably) I am getting error messages about duplicate values. 

Any advice greatly appreciated. 

[vicky_]

Depending on why you need to summarize, you might not need to use a calculation for it: 

If you do need to create a summary, you can consider using something like 

Summarized = SUMMARIZE('Table', 'Table'[Product], "First Category", CALCULATE(MIN('Table'[Shop category]))

Just a note: the MIN takes the first product alphabetically. If you have some index in your raw data, it's best that you use that in the calculation.