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Define a Function that Flattens Data in a List

When presented with nested structures of data, you might need to reduce (or "flatten") the data in them to produce a simpler output. Before you begin, note that DataWeave 2.0 (%dw 2.0) is for Mule 4 apps. For a Mule 3 app, refer to DataWeave 1.0 (%dw 1.0) examples, within the Mule 3.9 documentation set. For other Mule versions, you can use the Mule Runtime version selector in the table of contents.

This DataWeave example flattens the data in the interests and contenttypes arrays with the function that is defined in the header, and it only outputs contenttypes when it is not empty.

The example uses these functions:

  • map to go through a set elements in the input.

  • reduce to flatten the arrays.

  • if to conditionally display a field.

  • splitBy to parse the input.

DataWeave
%dw 2.0
output application/json
fun reduceMapFor(data) = data reduce (($$ splitBy ":")[0] ++ "," ++ ($ splitBy ":")[0])
---
payload.results map() ->
{
  email: $.profile.email,
  name: $.profile.firstName,
  tags: reduceMapFor($.data.interests.tags[0]),
        (contenttypes: reduceMapFor($.data.interests.contenttypes[0])) if(sizeOf($.data.interests.contenttypes[0]) > 0)
}
Input JSON
{
  "results": [
    {
      "profile": {
        "firstName": "john",
        "lastName": "doe",
        "email": "johndoe@demo.com"
      },
      "data": {
        "interests": [
          {
            "language": "English",
            "tags": [
              "digital-strategy:Digital Strategy",
              "innovation:Innovation"
            ],
            "contenttypes": []
          }
        ]
      }
    },
    {
      "profile": {
        "firstName": "jane",
        "lastName": "doe",
        "email": "janedoe@demo.com"
      },
      "data": {
        "interests": [
          {
            "language": "English",
            "tags": [
              "tax-reform:Tax Reform",
              "retail-health:Retail Health"
            ],
            "contenttypes": [
              "News",
              "Analysis",
              "Case studies",
              "Press releases"
            ]
          }
        ]
      }
    }
  ],
  "objectsCount": 2,
  "totalCount": 2,
  "statusCode": 200,
  "errorCode": 0,
  "statusReason": "OK"
}
Output JSON
[
  {
    "email": "johndoe@demo.com",
    "name": "john",
    "tags": "digital-strategy,innovation"
  },
  {
    "email": "janedoe@demo.com",
    "name": "jane",
    "tags": "tax-reform,retail-health",
    "contenttypes": "News,Analysis,Case studies,Press releases"
  }
]

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