Average Top 50 Percentile Values in an Array

I'm trying to figure out a formula that will find the average of the top 50th percentile of a data set.

Example:
Data Set:
1
2
3
4
5
6

Top 50th percentile {4,5,6}
average(4,5,6)=5

There is an excel formula "percentile" but it only returns the 50th percentile value, not a data set that I can average.

Thanks you guys, that is what I was looking for. I did find an instance where it was not returning the expected result though. For example if the data set is {2,1,0,0,0,0} then this formula will return the result "0.5" but what I would like it to return would be the value "1" (it is taking the average of all the values since the 50th percentile is "0" instead of just the first three like I would like). Could I use a different formula to just take the average of the top half of the values instead of >= 50th percentile? The numbers might not be in order so that might make it more challenging. What do you think?

Thanks Martin, that was very helpful.

I've got one more bonus question on this since you seem to be so good at it . This one could be challenging but here goes. From our ERP system we can get a report that shows the quantity of product shipped by customer by month. From this I would like to be able to find the average for each customer, the average for the month, and the average for the top 50% in a month (using the logic in your second set of formulas).

The one challenging part to it is that our ERP system won't return a zero value if there are no sales in a given month, it will instead return a blank cell. This is problematic because you might have a new customer come in three months ago and his monthly sales quantity will be {2,0,2} but the six month report will show {-,-,-,2,-,2} and I would only want to take the average of {2,0,2}. I've attached a sample worksheet of how the data could look. The green cells are cells that I would want used in the calculation and the white ones I would not, the yellow ones are where the results would show. What do you think?

Sample Average Worksheet.xlsx