Merge two json payload with dataweave - mule

Question

I have a Mule flow that calls two REST API's resulting in two json list payloads. I need to obtain a merged json list from these two payloads.
I managed to achieve this with a scatter-gather flow with a custom aggregator strategy. However the code I had to write for this looks rather messy and it's slow.
Is there any way to achieve this using dataweave?`
input Json list 1:
[{
"ID": "1",
"firstName": "JANE""familyName": "DOE",
"Entities": [{
"ID": "515785",
"name": "UNKOWN UNITED",
"callSign": "UU"
}]
},
{
"ID": "2",
"firstName": "JOHN",
"familyName": "DOE",
"Entities": [{
"Entities_ID": "515785",
"name": "UNKOWN UNITED",
"callSign": "UU"
}]
}]
input Json list 2:
[{
"ID": "1",
"firstName": "JANE",
"familyName": "DOE",
"Entities": [{
"Entities_ID": "8916514",
"name": "UNKOWN INCORPORATED",
"callSign": "UI"
}]
},
{
"ID": "4",
"firstName": "JAKE",
"familyName": "DOE",
"Entities": [{
"Entities_ID": "8916514",
"name": "UNKOWN INCORPORATED",
"callSign": "UI"
}]
}]
desired output is a merged list without duplicate IDs:
[{
"ID": "1",
"firstName": "JANE",
"familyName": "DOE",
"Entities": [{
"Entities_ID": "515785",
"name": "UNKOWN UNITED",
"callSign": "UU"
},
{
"Entities_ID": "8916514",
"name": "UNKOWN INCORPORATED",
"callSign": "UI"
}]
},
{
"ID": "2",
"firstName": "JOHN",
"familyName": "DOE",
"Entities": [{
"Entities_ID": "515785",
"name": "UNKOWN UNITED",
"callSign": "UU"
}]
},
{
"ID": "4",
"firstName": "JAKE",
"familyName": "DOE",
"Entities": [{
"Entities_ID": "8916514",
"name": "UNKOWN INCORPORATED",
"callSign": "UI"
}]
}]

Answer 1

This works for me with dataweave where payload is list1 and flowVars.list2 is list2
%dw 1.0
%output application/json
%var mergeddata = flowVars.list2 groupBy $.ID
---
payload map ((data,index) -> {
ID: data.ID,
firstName : data.firstName,
familyName : data.familyName,
Entities : data.Entities ++ (mergeddata[data.ID].Entities default [])
}) ++
(flowVars.list2 filter (not (payload.ID contains $.ID)))
Hope this helps