<p dir="auto">Following up on <a class="issue-link js-issue-link" data-error-text="Failed to load title" data-id="196267978" data-permission-text="Title is private" data-url="https://github.com/scikit-learn/scikit-learn/issues/8075" data-hovercard-type="pull_request" data-hovercard-url="/scikit-learn/scikit-learn/pull/8075/hovercard" href="https://github.com/scikit-learn/scikit-learn/pull/8075">#8075</a> I think we should have a convenience option to add <code class="notranslate">MissingIndicator</code> to <code class="notranslate">SimpleImputer</code> without having to build a <code class="notranslate">FeatureUnion</code> or <code class="notranslate">ColumnTransformer</code>.</p>
<p dir="auto">For whatever imputers we have, but especially <a href="http://scikit-learn.org/dev/modules/generated/sklearn.impute.SimpleImputer.html" rel="nofollow">SimpleImputer</a>, we should have an <code class="notranslate">add_indicator</code> parameter, which simply stacks a <a href="http://scikit-learn.org/dev/modules/generated/sklearn.impute.MissingIndicator.html" rel="nofollow">MissingIndicator</a> transform onto the output of the imputer's <code class="notranslate">transform</code>.</p>