How to calculate average only for certain values?

[Anonymous]

So I have inherited from another user a table with a couple of columns that calculate the difference between two other columns and then replaces all negative values with zero, as follows:

Column C = datediff('Table'[Column B].[Date],'Table'[Column A].[Date],DAY))

Column D = if('Table'[Column C]>0,'Table'[Column C],0)

There is then a visual which displays the average of Column D via the following Measure:

Measure = CALCULATE(AVERAGE(Table[Column D]))

The problem with this is that the zeroes in Column D are artificially pulling the average down (Column D is a "days late" kind of metric, so we shouldn't be including zeroes). How can I go about changing the measure to only calculate the average for non-zero values? I tried using FILTER and WHERE statements as follows with no success (syntax errors):

Measure = WHERE(Table[Column D]>0),CALCULATE(AVERAGE(Table[Column D]))

Measure = CALCULATE(AVERAGE(FILTER(Table,[Column D]>0)))

It is probably pretty obvious from my question that I am a complete newbie to DAX syntax. Could someone please help? I'm sure there's probably a MUCH simpler way of accomplishing this task, I just don't know the language to do it. Thanks in advance!

[Anonymous · Accepted solution]

Of what I can make from you starting text the measure should be something like this:

DIVIDE(
SUM('Table'[Column D]),
CALCULATE(COUNT('Table'[Column D]),FILTER(ALL(Table);'Table'[Column D] >0))
)