title: sklearn model_selection Error: ImportError: cannot import name '_approximate_mode'
body: <p>I'm trying to import sklearn model_selection but I'm getting the following error:</p>
  
  <pre><code>ImportError                               Traceback (most recent call last)
  &lt;ipython-input-219-6bc6f0a77ca9&gt; in &lt;module&gt;()
  ----&gt; 1 import sklearn.model_selection
  
  ~/anaconda3/lib/python3.6/site-packages/sklearn/model_selection/__init__.py in &lt;module&gt;()
  ----&gt; 1 from ._split import BaseCrossValidator
        2 from ._split import KFold
        3 from ._split import GroupKFold
        4 from ._split import StratifiedKFold
        5 from ._split import TimeSeriesSplit
  
  ~/anaconda3/lib/python3.6/site-packages/sklearn/model_selection/_split.py in &lt;module&gt;()
       21 
       22 from ..utils import indexable, check_random_state, safe_indexing
  ---&gt; 23 from ..utils import _approximate_mode
       24 from ..utils.validation import _num_samples, column_or_1d
       25 from ..utils.validation import check_array
  
  ImportError: cannot import name '_approximate_mode'
  </code></pre>
  
  <p>I tried uninstalling scikit-learn and reinstalling it but I get the same error. My current version of scikit-learn is 0.21.2.
  Thanks for the help!</p>