# Mutate the value where Key Equal

 Mutate the value of a key.

## Example

This example shows how to use the MutateValueWhereKeyEq transformation to mutate the value of a key if the key exists.

```json
{
	"operation": "mutate_value_where_key_eq",
	"arguments": {
		"key": "field1",
		"value": "new_value"
	}
}
```

Given the input record:

```json
{
	"field1": "old_value",
	"another_field": "another_value"
}
```

The output record will be:

```json
{
	"field1": "new_value",
	"another_field": "another_value"
}
```

If the key does not exist:

Given the input record:

```json
{
	"field2": "some_value",
	"another_field": "another_value"
}
```

The output record will be unchanged:

```json
{
	"field2": "some_value",
	"another_field": "another_value"
}
```