<h4 dir="auto">Description</h4>
<p dir="auto"><code class="notranslate">sklearn.utils.multiclass</code>  <code class="notranslate">unique_labels()</code> does not yet allow <code class="notranslate">"multiclass-multioutput"</code> input type for <code class="notranslate">y</code> .<br>
See this comment in the code: </p><div class="Box Box--condensed my-2">
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      <a href="https://github.com/scikit-learn/scikit-learn/blob/3a48f0ab7cf75dea55f313da6b33f7b6772d28af/sklearn/utils/multiclass.py#L53">scikit-learn/sklearn/utils/multiclass.py</a>
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          <td id="LC53" class="blob-code border-0 px-3 py-0 color-bg-default blob-code-inner js-file-line"> <span class="pl-s">    At the moment, we also don't allow "multiclass-multioutput" input type.</span> </td>
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<p dir="auto">This type is used by multilabel classifiers such as <code class="notranslate">sklearn.tree.DecisionTreeClassifier</code>.<br>
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      <a href="https://github.com/scikit-learn/scikit-learn/blob/4bba21659c68d65b4555ea86751aac1fab9fd8e4/sklearn/tree/tree.py#L763">scikit-learn/sklearn/tree/tree.py</a>
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          <td id="LC763" class="blob-code border-0 px-3 py-0 color-bg-default blob-code-inner js-file-line"> <span class="pl-s">        y : array-like, shape = [n_samples] or [n_samples, n_outputs]</span> </td>
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<p dir="auto">So I propose to add support for this.  At first glance, it doesn't appear to be difficult. Is there any reason not to to this?</p>
<p dir="auto">It looks to me like the decision trees use <code class="notranslate">accuracy_score</code> for their <code class="notranslate">score</code> but <code class="notranslate">accuracy_score</code> doesn't document that it's supporting <code class="notranslate">multiclass-multioutput</code> which the trees do.</p>
<p dir="auto"><del>I guess the <code class="notranslate">y_true == y_pred</code> works in this case, but it should be documented.<br>
There's no list of scores supporting multiclass-multioutput in the docs, and that should be fixed, too.</del></p>
<p dir="auto">Update:<br>
Calling <code class="notranslate">score</code> in this case errors :-/</p>