Provide count distinct functionality

[TheCaffinatedDeveloper]

We have been loving the ZEN rules engine and it's ease of use. The javascript function "escape hatch" is quite nice and allows for some extensive capabilities. I will say however, the ability to count distinct elements in an array would be much appreciated.

My recommendations: if the element in the array is a "zen primitive" such as number, date, string etc it should be fairly straightforward (and perhaps that's the first support). If its a context then the user could provide a callback that returns a string of concatenated properties that make this context unique etc.

I know this can be done using javascript functions but it would be nice to be able to do count_distinct([date, date, date]) out of the box to calculate number of distinct dates for example. Or len(distinct([date, date, date]))

[ivanmiletic]

Good suggestion, added to backlog

[hatbrox]

use len + indexOf

My customer has made 10 product purchases and I want to count how many distinct product were bought on week end only (I added week end for extra fun).

source data:

{
  "customer": {
    "purchases": [
      { "name": "Product A", "purchaseDate": "2025-06-30" }, // Monday
      { "name": "Product B", "purchaseDate": "2025-07-01" }, // Tuesday
      { "name": "Product C", "purchaseDate": "2025-07-05" }, // Saturday
      { "name": "Product D", "purchaseDate": "2025-07-06" }, // Sunday
      { "name": "Product E", "purchaseDate": "2025-07-03" }, // Thursday
      { "name": "Product C", "purchaseDate": "2025-07-06" }, // Sunday
      { "name": "Product G", "purchaseDate": "2025-06-29" }, // Sunday
      { "name": "Product H", "purchaseDate": "2025-06-28" }, // Saturday
      { "name": "Product I", "purchaseDate": "2025-07-02" }, // Wednesday
      { "name": "Product J", "purchaseDate": "2025-07-04" }  // Friday
    ]
  }
}

zen expression:

len(
  filter(
    map(
      filter(customer.purchases, # => dayOfWeek(date(#.purchaseDate)) in [6, 7]),
      #.name
    ),
    (x, i, arr) => indexOf(arr, x) == i
  )
)

result:
Qty of "Product C" => 2
Qty of all other products (D, G and H) => 1 each.

in total 5 products were purchased on the week end
but only 4 distinct products were purchased on the week end

[bknoles]

Did the API change? I'm getting an error on a local build of the editor when supplying a callback form like (x, i, arr) => indexOf(arr, x) == i, and the docs only show a # > 1 type of callback.