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# MLMetricKey

A key for the metrics dictionary in an update context.

```
class MLMetricKey
```

## Topics

### Getting the keys

[`lossValue`](/documentation/CoreML/MLMetricKey/lossValue)

The key you use to access the current loss (a `float` value).

[`epochIndex`](/documentation/CoreML/MLMetricKey/epochIndex)

The key you use to access the epoch index (an `Int64` value).

[`miniBatchIndex`](/documentation/CoreML/MLMetricKey/miniBatchIndex)

The key you use to access the mini-batch index (an `Int64` value) within an epoch.

### Supporting types

[`MLKey`](/documentation/CoreML/MLKey)

An abstract base class for machine learning key types.


---

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