How to merge two lists based on a matching string and assign incremental numbers to each object using Mulesoft DataWeave

How can I merge the following two lists ids and attributes based on the matching did field and for each matched pair increment the iterid values

For example I have two lists below. size of the list differ dynamically

ids

[
  {
    "id": "d3c0da07-e58f4606bm",
    "did": "714c9836927d"
  }
]

attributes

[
  {
    "snm": "3298SJDJ",
    "did": "714c9836927d"
  }
]

I want to achieve the result like below

[
  {
    "iterid": 1,
    "id": "d3c0da07-e58f4606bm",
    "did": "714c9836927d"
  },
  {
    "iterid": 2,
    "id": "d3c0da07-e58f4606bm",
    "did": "714c9836927d"
  }
]

I've tried with flatMap to form the merged list, but I'm being blocked at incrementing the iterid count dynamically

You can do it with same flatMap along with adding a logic to increment a number by leveraging the index of the elements in each iteration.

Here is the example below

%dw 2.0
output application/json

var ids = [
  {
    "id": "d3c0da07-e58f4606bm",
    "did": "714c9836927d"
  }
]

var attributes = [
  {
    "snm": "3298SJDJ",
    "did": "714c9836927d"
  }
]

var data = ids flatMap ((id) ->
  (attributes filter ((attribute) -> attribute.did == id.did))
    map ((attribute) -> {
      snm:  attribute.snm,
      did:  id.did,
      id:   id.id
    })
)

---
data flatMap ((item, index) -> [
  {
    iterid: (index * 2) + 1,
    id: item.id,
    did: item.did
  },
  {
    iterid: (index * 2) + 2,
    id: item.id,
    did: item.did
  }
])