title: why scikit-learn StandardScaler doesnt support keep_nan operation?
body: <p>when I want to do machine learning project, i want to scale my input into (0,1)</p>
  <p>I use sklearn function to do that, such as StandScaler()
  but i found once my data contains nan, fit_transform() will fail, as following:</p>
  <pre><code>ValueError: Input contains NaN, infinity or a value too large for dtype('float64').
  </code></pre>
  <p>but i think there is some kind of need, wants to keep nan, and do standard scale in other not nan data.</p>
  <p>why sklearn dont support that? Is there any methods to use it?</p>