How to group by a field in an object to create an array of objects?

Question

I have an input payload containing array of objects where I need to group-by id-key and form 2 arrays of objects based on id-key. See below details.

input Payload:

{
  "id": {
    "header_id": "460",
    "id-branch": {
      "branch-name": "genaral motors",
      "req-name": "genaral motors",
      "id-key": "0791",
      "id-lines": {
        "id-key": "0791",
        "productId": "463"
      }
    },
    "id-branch": {
      "branch-name": "genaral motors",
      "req-name": "genaral motors",
      "id-key": "9692",
      "id-lines": {
        "id-key": "9692",
        "productId": "464"
      },
      "id-lines": {
        "id-key": "9692",
        "productId": "465"
      }
    }
  }
}

desired Ouput:

[                      
 {
  "branch-name": "genaral motors",
  "req-name": "genaral motors",
  "type": "dhl",
  "lines-ids": "swr",
  "lines": [
    {
      "productId": "463"
    }
  ]
 },
 {
  "branch-name": "genaral motors",
  "req-name": "genaral motors",
  "type": "dhl",
  "lines-ids": "swr",
  "lines": [
    {
      "productId": "464"
    },
    {
      "productId": "465"
    }
  ]
 }
]

the output has to be generated as array of object which groups productId which are under same id-key.

Answer 1

Assuming that the keys are already grouped by product id, I used filterObject() to remove the keys that are not required, then use pluck() to pick the values into an array. After that I removed keys from each element that are not used in the output. The keys added I assumed that were literal since no indication was given. For clarity I implemented a function to encapsulate the mapping of the lines.

%dw 2.0
output application/json
fun updateLines(x)=
    x - "id-lines" ++ {lines: x.*"id-lines" map {productId: $.productId}}
---
payload.id
    filterObject ((value, key, index) -> key as String == "id-branch")
    pluck ($) 
    map (updateLines($) - "id-key" ++ { "type": "dhl", "lines-ids": "swr"})

Output:

[
  {
    "branch-name": "genaral motors",
    "req-name": "genaral motors",
    "lines": [
      {
        "productId": "463"
      }
    ],
    "type": "dhl",
    "lines-ids": "swr"
  },
  {
    "branch-name": "genaral motors",
    "req-name": "genaral motors",
    "lines": [
      {
        "productId": "464"
      },
      {
        "productId": "465"
      }
    ],
    "type": "dhl",
    "lines-ids": "swr"
  }
]