If won, then calculate difference between two dates

[lguelcher]

I'm trying to add a calculated column to calculate the number of days between two dates. However, I need to only calculate for those that meet a certain criteria. 

The formula I tried is: 

DiffCloseDate = if(Opportunities[Status]="won",(Opportunities[Actual Close Date]-Opportunities[Est Close Date]),"")

For the 'then' clause, I also tried

Datediff(Opportunities[Est Clsoe Date],Opportunities[Actual Close Date],Days)

The error I'm receiving is:

A single value for column 'Actual Close Date' in table Opportunities cannot be determined. This can happen when a measure formula refers to a column that contains many values without specifying an aggregation such as min, max, count, or sum to get a single result.

But, I don't want to aggregate the dates. I just want each row to perform the calculation.

Thanks for any help.

[Greg_Deckler · Accepted solution]

Are you sure that you are using a calculated column because the error you are getting is for a measure. If you use a calculated column, your formula would generate an error regarding "variant" data because you are trying to return a number and a string at the same time. Both have to agree in terms of the data type returned. So, you could do something like this as a calculated column (not a measure)

DiffCloseDate = IF(Opportunities[Status]="won",Opportunities[Actual Close Date]-Opportunities[Est Close Date],-999)

[greggyb]

@lguelcher, are you defining this column in the 'Opportunities' table?