Multiclasshammingdistance

multiclasshammingdistance

Metric MulticlassHammingDistance from torchmetrics (torchmetrics.classification.MulticlassHammingDistance)

When to invoke this skill

The user has predictions + ground truth and asks to evaluate with MulticlassHammingDistance, or mentions torchmetrics.classification.MulticlassHammingDistance directly, or wants the standard torchmetrics implementation.

Reference signature

from torchmetrics.classification import MulticlassHammingDistance

# MulticlassHammingDistance(num_classes: Optional[int] = None, top_k: int = 1, average: Optional[Literal['micro', 'macro', 'weighted', 'none']] = 'macro', multidim_average: Literal['global', 'samplewise'] = 'global', ignore_index: Optional[int] = None, validate_args: bool = True, **kwargs: Any) -> None

Library docstring

Compute the average `Hamming distance`_ (also known as Hamming loss) for multiclass tasks.

.. math::
    \text{Hamming distance} = \frac{1}{N \cdot L} \sum_i^N \sum_l^L 1(y_{il} \neq \hat{y}_{il})

Where :math:`y` is a tensor of target values, :math:`\hat{y}` is a tensor of predictions,
and :math:`\bullet_{il}` refers to the :math:`l`-th label of the :math:`i`-th sample of that
tensor.

As input to ``forward`` and ``update`` the metric accepts the following input:

- ``preds`` (:class:`~torch.Tensor`): An int tensor of shape ``(N, ...)`` or float tensor of shape ``(N, C, ..)``.
  If preds is a floating point we apply ``torch.argmax`` along the ``C`` dimension to automatically convert
  probabilities/logits into an int tensor.
- ``target`` (:class:`~torch.Tensor`): An int tensor of shape ``(N, ...)``.

As output to ``forward`` and ``compute`` the metric returns the following output:

- ``mchd`` (:class:`~torch.Tensor`): A tensor whose returned shape depends on the ``average`` and
  ``multidim_average`` arguments:

    - If ``multidim_average`` is set to ``global``:

      - If ``average='micro'/'macro'/'weighted'``, the output will be a scalar tensor
      - If ``average=None/'none'``, the shape will be ``(C,)``

    - If ``multidim_average`` is set to ``samplewise``:

      - If ``average='micro'/'macro'/'weighted'``, the shape will be ``(N,)``
      - If ``average=None/'none'``, the shape will be ``(N, C)``

If ``multidim_average`` is set to ``samplewise`` we expect at least one additional dimension ``...`` to be present,
which the reduction will then be applied over instead of the sample dimension ``N``.

Args:
    num_classes: Integer specifying the number of classes
    average:
        Defines the reduction that is applied over labels. Should be one of the following:

        - ``micro``: Sum statistics over all labels
        - ``macro``: Calculate statistics for each label and average them
        - ``weighted``: calculates statistics for each label and computes weighted average using their support
        - ``"none"`` or ``None``: calculates statistic for each label and applies no reduction
    top_k:
        Number of highest probability or logit score

Quick recipe

import torchmetrics.classification as _m
score = _m.MulticlassHammingDistance(y_true, y_pred)

Don'ts

• Don't reimplement when the library version handles edge cases (NaN, ties, empty inputs) better than a hand-rolled formula.
• Always check the library version's argument order — sklearn is (y_true, y_pred) while torchmetrics is (preds, target).