title: Sklearn Univariate Selection: Features are Constant
body: <p>I am getting the following warning message when trying to use Feature Selection and f_classif (ANOVA test) on some data in sklearn:</p>
  
  <p>C:\Users\Alexander\Anaconda3\lib\site-packages\sklearn\feature_selection\univariate_selection.py:113: UserWarning: Features ... are constant.
    UserWarning)</p>
  
  <p>The features that the warning message indicated were constant apparently had p-values of 0. I was unable to find any information about what was causing this warning. The github file for this particular function is here: <a href="https://github.com/scikit-learn/scikit-learn/blob/master/sklearn/feature_selection/univariate_selection.py" rel="noreferrer">https://github.com/scikit-learn/scikit-learn/blob/master/sklearn/feature_selection/univariate_selection.py</a></p>
  
  <p>Any help would be appreciated, thanks.</p>