> ## Documentation Index
> Fetch the complete documentation index at: https://docs.alumio.com/llms.txt
> Use this file to discover all available pages before exploring further.

# Array or object: Merge

> Merges the supplied data into the array or object. Existing keys are overwritten.

Use this mapper to combine the input with a set of data you supply, producing a single merged result. Where both sides share the same key, the value you supply wins and replaces the one from the input; keys that exist on only one side are kept as they are. The merge also reaches into nested objects, so you can update a field deep inside a structure without rewriting the whole thing. This is handy for adding fixed defaults or overriding a few fields on every record.

This documentation describes: [Schema](/schemas/mapper/list-extend-with)

## Fields

**Data**

Required

The data to merge in, entered directly as a small block of data in the form. Any key it shares with the input overwrites the input's value; any new key is added. The merge applies at every level, including nested objects.

## Sample data

This example overrides one attribute and adds a new one on a product's attributes.

| Field | Value |
| - | - |
| Data | `{ "size": "L", "material": "wool" }` |

Input:

```json theme={null}
{
    "color": "red",
    "size": "M"
}
```

Output:

```json theme={null}
{
    "color": "red",
    "size": "L",
    "material": "wool"
}
```

The `size` value is overwritten with `L`, the new `material` field is added, and `color` is left untouched.

```json Configuration theme={null}
{
  "prototype": "list-extend-with",
  "parameters": {
    "array": { "size": "L", "material": "wool" }
  }
}
```


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