Attribute Rules Arcade expression

[RandyMcGraw1]

Hello,

I'm trying to write an expression to count the number of values, for each type within a field (i.e. region A, region B) to populate a second field with the results, with Attribute Rules. So far I can select the region for each entry but I have not been able to filter the count for each entry by its region. My code so far: 

When ($feature.Region=='A',Count($feature.Region), $feature.Region=='B',Count($feature.Region),1000)

I tried using the filter but I could not get it to work.

Any suggestions?
Thanks

Randy 

[Justin_Greco]

You are on the right track using the Filter function.  In your code, the Count is just returning the number of characters in the Region field for the $feature, which will always be 1 since its either A or B.  You need to pass a FeatureSet into the Count to get a record count. For the Filter function, I am passing $layer, which is the layer the $feature belongs to.  Then I am filtering the features that have the same Region as the $feature and getting the count.

return Count(Filter($layer, "Region = '"+$feature.Region+"'"))

[RandyMcGraw1]

Thanks Justin_Greco, I believe your expressions is correct but since I am using ArcGIS pro 2.7.1 it does not recognize $layer. I am looking with my IT department to see if I can update my pro version to 3.2 which would allow me to use your expression. 

Thanks again

[Justin_Greco]

$layer might not be available for attribute rule profile, so I think you can use FeatureSetByName, I'm not sure what your layer name is, so replace "Regions" with your layer's name.

var fs = FeatureSetByName($datastore, "Regions")
return Count(Filter(fs, "Region = '"+$feature.Region+"'"))