Hi Reeza. Thank you for the promt reply.
There are all data for 6 month for the Medium aircraft in the data set- so the 'average daily flights' (number of flights) for the period 'Up-to 30June' are calculate correctly in Summary Table in this case.
As for the Heavy aircraft then there are data just for 1month in 2012 and 2 month in 2013 in the data set. The other months are presented by missing value in the Summary Table. The function MEAN takes in to the account just months with nonmissing values when calculates the 'average daily flights' for the period 'Up-to 30June' - the result is not correct in this case. Actually the value for the other month must be 0, you are right, but only for row ˇ average daily flightsˇ . Averages for MTOW (weight of aircraft) are calculated for the months with nonmissing data and it is right.
Of course, I could add the rows with other months to the data set, but I think it is not the nice solution. I would prefer to have some function like 'meanmiss' or 'meanall' to solve this problem in the Summary table ,but I have not found anything like this.
Could anybody propose your own approach to solve this problem ?