# Flatten

 Flatten a nested map or array into a flat map.

## Example

This example shows how to use the Flatten transformation to flatten a nested structure within a JSON record.

```json
{
  "operation": "flatten",
  "arguments": {
    "key": "nested_data",
    "base": "flattened",
    "delimiter": "_"
  }
}
```

Given the input record:

```json
{
  "nested_data": {
    "level1": {
      "level2": {
        "value": 42
      },
      "array": [1, 2, 3]
    }
  }
}
```

The output record will be:

```json
{
  "flattened.nested_data_level1_level2_value": 42,
  "flattened.nested_data_level1_array_0": 1,
  "flattened.nested_data_level1_array_1": 2,
  "flattened.nested_data_level1_array_2": 3
}
```