How to combine two arrays using flatten in DataWeave

Let us consider a scenario where two simple sub-arrays need to be combined into a single array using Mule 4 DataWeave. We can achieve this very simply using the flatten function in DataWeave 2.0.

What is the use of flatten in DataWeave?

Converts a set of subarrays (such as [ [1,2,3], [4,5], [null] ]) into a single, flattened array (such as [ 1, 2, 3, 4, 5, null ])

Note: The null arrays will be excluded in the output

Also Read: 12 Useful list of Predefined variables in Dataweave MuleSoft

Combine two arrays into a single JSON array using DataWeave flatten

Input:

[
   [
      {
         "key":"abc"
      },
      {
         "key":"def"
      }
    
   ],
   [
      {
         "key":"123"
      },
      {
         "key":"456"
      }
  
   ]
]

Output:

[
  {
    "key": "abc"
  },
  {
    "key": "def"
  },
  {
    "key": "123"
  },
  {
    "key": "456"
  }
]

DataWeave Code:

%dw 2.0
output application/json
---
flatten(payload)

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