Suggestion: Remove prediction from plot_confusion_matrix and just pass predicted labels

The signature of plot_confusion_matrix is currently:

sklearn.metrics.plot_confusion_matrix(estimator, X, y_true, labels=None, sample_weight=None, normalize=None, display_labels=None, include_values=True, xticks_rotation='horizontal', values_format=None, cmap='viridis', ax=None)

The function takes an estimator and raw data and can not be used with already predicted labels. This has some downsides:

• If a confusion matrix should be plotted but the predictions should also be used elsewhere (e.g. calculating accuracy_score) the estimation has to be performed several times. That takes longer and can result in different values if the estimator is randomized.
• If no estimator is available (e.g. predictions loaded from a file) the plot can not be used at all.

Suggestion: allow passing predicted labels y_pred to plot_confusion_matrix that will be used instead of estimator and X. In my opinion the cleanest solution would be to remove the prediction step from the function and use a signature similar to that of accuracy_score, e.g. (y_true, y_pred, labels=None, sample_weight=None, ...). However in order to maintain backwards compatibility, y_pred can be added as an optional keyword argument.

TODO:

• Introduce the class methods for the currently existing plots:

  • ConfusionMatrixDisplay https://github.com/scikit-learn/scikit-learn/pull/18543
  • PrecisionRecallDisplay https://github.com/scikit-learn/scikit-learn/pull/20552
  • RocCurveDisplay https://github.com/scikit-learn/scikit-learn/pull/20569
  • DetCurveDisplay https://github.com/scikit-learn/scikit-learn/pull/19278
  • PartialDependenceDisplay. For this one, we don’t want to introduce the from_predictions classmethod because it would not make sense, we only want from_estimator.

• For all Display listed above, deprecate their corresponding plot_... function. We don’t need to deprecate plot_det_curve because it hasn’t been released yet, we can just remove it.

• for new PRs like #17443 and #18020 we can implement the class methods right away instead of introducing a plot function.

[jnothman]

One classic pattern for this kind of thing is defining:

ConfusionMatrixDisplay.from_estimator(...)
ConfusionMatrixDisplay.from_predictions(...)

but this is not very idiomatic to scikit-learn.

[glemaitre]

I will take care of the other classes then and advance my stalled PR. @lucyleeow in case I did not do all of those and you are searching for some PRs, ping me 😃