How to Calculate the median, from the Value of Rule Inputs for individual item in an Cascading dropdown

Question

Hello Everyone, 
 I have an editable Grid, which contains a Cascading Drop down as shown below, where as the category displays 'MI' and Skills pop up related to that. I also have multiple values as such. And i can add more rows to it. 
 
 The following is the Rule Input 
 
 Now, how can I to have a median calculated based on "ri!CC_Person.skills.Rating" only for 'MI' even though I add more rows and select 'MI' with the rating. 
 Thanks in advance..!!

Ashvin Kapur · Answer

Can you index the list of CC_Person wherecontains MI for skills.category? Something like: 
 
median(index(ri!CC_Person.skills.rating, wherecontains("MI", ri!CC_Person.skills.category), 0)) 
 
I'd have to test the code to know if it works correctly, so let me know if that still doesn't work and we can discuss in more detail.

Ashvin Kapur · Answer

Not sure I understand - why would you need the forEach() at all? Seems like you want the median of ALL ratings where the category is MI. Try this: 
 
a!textField( 
 value: median(index(ri!CC_Person.skills.rating, wherecontains("MI", ri!CC_Person.skills.category), 0)), 
 readOnly: true() 
) 
 
I also sent you a message, so let me know offline if you need additional info from me. This seems to just be a logic configuration question which we can handle off of the message board.

Joubin Izadi · Answer

Try this updated version of Ashvin's code. I've added some safeguards here, the main one being: 
 Indexing instead of using dot notation - As stevens812 noted, if ri!CC_Person.skills is null (not typed), we would get the error you posted. By indexing, we avoid the UI error. 
 a!textField(
 value: median(
 index(
 index(ri!CC_Person.skills, "rating", {}), 
 wherecontains(
 "MI", 
 touniformstring(index(ri!CC_Person.skills, "category", {}))
 ), 
 0
 )
 ),
 readOnly: true()
)