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title: Map and Flatten an Array
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---

# Map and Flatten an Array

> For the full documentation index, see: https://docs.mulesoft.com/llms.txt

The `flatMap` function calls `map` on an input and wraps the results in a call to `flatten`.

The `flatMap` function is useful for refactoring uses of `flatten` on the results of a call to
`map`. For example, review the following DataWeave script:

DataWeave Script:

```dataweave
%dw 2.0
output application/json
var myData = [{name:1},{name:2},{name:3}]
fun myExternalFunction(data): Array =
    if(data.name == 1)
        []
    else if(data.name == 2)
        [{name: 3}, {name:5}]
    else
        [data]
---
//flatten(myData map ((item, index) -> myExternalFunction(item)))
myData flatMap ((item, index) -> myExternalFunction(item))
```

The header of the script creates a variable `myData` to define an array of objects, each with the
key `name`. It also defines a function with a set of if-else statements that act on name-value pairs
with the key `name`.

The body of the DataWeave script contains the following expressions, each of which produces the same
result:

- `flatten(myData map ((item, index) → myExternalFunction(item)))`

- `myData flatMap ((item, index) → myExternalFunction(item))`

Whether you use the `flatMap` expression or explicitly use `flatten` to wrap the `map` expression,
the following takes place:

1.  The expression maps the items in the input array according to if-else conditions in the function
    `myExternalFunction()`, which is defined in the header.

    The mapping produces the following output:

    ```json
    [[], [{ "name": 3 }, { "name": 5 }], [{ "name": 3 }]]
    ```

2.  The expression flattens the mapped results by consolidating the elements from the subarrays into
    a single array, removing the parent array and eliminating the empty child array.

    Flattening produces the following output:

    Output JSON:

    ```json
    [
      {
        "name": 3
      },
      {
        "name": 5
      },
      {
        "name": 3
      }
    ]
    ```

## See Also

- [flatMap](https://docs.mulesoft.com/dataweave/2.4/dw-core-functions-flatmap)