Averaging using filter

[ABookbin]

Hi All, 

I'm trying to add a column in the table below which provides an average value according to city-city pair. Here's what I have right now.

Here are the average values I would like to see.

The code I have been using is: 

CALCULATE(AVERAGE('Air Shipment Tracking'[Actual Transit Days]),KEEPFILTERS('Air Shipment Tracking'[City-City Pair]))

but this returns me with a blank screen. 

Basically I want a column that provides me with an average transit time for a city-city pair, which I can compare to the actual transit time. 

Thanks!

[PaulOlding · Accepted solution]

Does this work?

CALCULATE(

AVERAGE('Air Shipment Tracking'[Actual Transit Days]),

ALLEXCEPT('Air Shipment Tracking', 'Air Shipment Tracking'[City-City Pair])

)