Find Key with min value and calc average value with that key

[#1]

Need help ))

I want to find min value in a table, than find a key for that value and after find average value for that key

i thought this is common taks but failed to find an answer

1/ Variable to find key with min value

MinString({$<HotelCost = {$(=Min(HotelCost))}>} RoomCategoryName)

Then i put this in expressions
=$(vHotelBaseRoom)

2/  Then i try to calc average value with that key

=Avg({$<RoomCategoryName={$(=$(vHotelBaseRoom))}}>} HotelCost)

Receive NULL

[#2]

Dear all, I found an answer for my problem by myself - Subset does not include current row context - that's why when i apply variable - i find min price room name
but this room name is not for this hotel and then i dont get anything

So i found my error - if you want to find minimum using this context then you nee to use if else expression