Iterates over an array and returns the unique elements in it. DataWeave uses the result of applying the provided lambda as the uniqueness criteria. This version of distinctBy finds unique values in an array. Other versions act on an object and handle a null value.

This function is useful for when you need to remove duplicate items from an Array. Here’s the function signature:

distinctBy(Array<T>, ((T, Number) -> Any)): Array<T>

Aside from the lambda returning Any, this function signature is identical to filter. The lambda passed to distinctBy should return a value that is unique to each item in the input Array.

Input

[
  {"id": "1", "environment": "dev"},
  {"id": "2", "environment": "test"},
  {"id": "3", "environment": "uat"},
  {"id": "4", "environment": "prod"},
  {"id": "2", "environment": "test"}
]

DW Script

%dw 2.0
output json
---
payload distinctBy $.id

Output

[
  {"id": "1", "environment": "dev"},
  {"id": "2", "environment": "test"},
  {"id": "3", "environment": "uat"},
  {"id": "4", "environment": "prod"}
]

---

When distinctBy finds a duplicate, does it use the original value in the output, or the found duplicate value? You can change the item value for one of the mouth wash Objects to find out.

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