How to calculate average price with FabCar

You can use GetHistoryForKey() to retrieve all the cars and next calculate the average price ciclying on them.

Supposing you want to know the maximum price you can do:

resultsIterator, err := stub.GetHistoryForKey(id)
    if err != nil {
        return shim.Error('Error')
    }

var max = nil;
for resultsIterator.HasNext() {
        response, err := resultsIterator.Next()

        if err != nil {
            return shim.Error(err.Error())
        }

        if (response.Value.Price > max)
           max = response.Value.Price
}

return shim.Success(max)

Something like this in Go. Easy to change in average price.