Mulesoft DataWeave: Transform flat list - mule

Question

I am relatively new to DataWeave, and was wondering how/if I can transform a message like below using DataWeave instead of a Java transformer.
If I have the following JSON payload of users, with a group and subgroup:
[{
"GROUP": "GROUP_A",
"SUBGROUP": "SUBGROUP A1",
"USER": "USER 1"
}, {
"GROUP": "GROUP_B",
"SUBGROUP": "SUBGROUP B1",
"USER": "USER 1"
}, {
"GROUP": "GROUP_B",
"SUBGROUP": "SUBGROUP B1",
"USER": "USER 2"
}, {
"GROUP": "GROUP_B",
"SUBGROUP": "SUBGROUP B2",
"USER": "USER 3"
}, {
"GROUP": "GROUP_B",
"SUBGROUP": "SUBGROUP B2",
"USER": "USER 4"
}, {
"GROUP": "GROUP_B",
"SUBGROUP": "SUBGROUP B2",
"USER": "USER 5"
}]
What would a DataWeave transformation look like to tranform the payload to something structured like the following:
[
{
"GROUP": "GROUP_A",
"SUBGROUPS": [{
"NAME": "SUBGROUP A1",
"USERS": ["USER 1"]
}]
}, {
"GROUP": "GROUP_B",
"SUBGROUPS": [{
"NAME": "SUBGROUP B1",
"USERS": ["USER 1", "USER 2"]
}, {
"NAME": "SUBGROUP B2",
"USERS": ["USER 3", "USER 4", "USER 5"]
}]
}
]
Thanks for any help!

Answer 1

For DataWeave development, please refer to DataWeave Reference Documentation. At this case You can refer to section Group by …. To transform above message, then try this script:
%dw 1.0
%output application/json
---
payload groupBy $.GROUP pluck {
GROUP: $$,
SUBGROUPS: $ groupBy $.SUBGROUP pluck {
NAME: $$,
USERS: $.USER
}
}