Filtering out duplicate values — where is my "count_distinct" function?

[jalter88]

I’m looking for a way to “count_distinct” values that are not a visible/selected dimension in my look. The function “count_distinct” I feel like would do the job perfectly. However, I get Unknown function “count_distinct” when I try to use it in my table calculation. Any help would be appreciated.

Full disclosure: I’m not particularly technical