title: Understanding Variance Treshold
body: <p>I am working on a text classification problem in python, where I build a traing array based on {0,1} if the word is inside the text or not.</p>
  
  <pre><code>array([[0., 1., 1., ..., 0., 0., 0.],
         [0., 1., 1., ..., 0., 0., 0.],
         [0., 1., 1., ..., 0., 0., 0.],
         ...,
         [0., 1., 1., ..., 0., 0., 0.],
         [0., 1., 1., ..., 0., 0., 0.],
         [0., 1., 1., ..., 0., 0., 0.]])
  </code></pre>
  
  <p>as I want to run SVM on it, I want to reduce my features. In scikit learn I found this: <a href="https://scikit-learn.org/stable/modules/feature_selection.html" rel="nofollow noreferrer">https://scikit-learn.org/stable/modules/feature_selection.html</a>
  with the Variance Threshold set to:</p>
  
  <pre><code>sel = VarianceThreshold(threshold=(.8 * (1 - .8)))
  x_train_red = sel.fit_transform(x_train)
  </code></pre>
  
  <p>from the reduction I am reducing my shape from:</p>
  
  <pre><code>(7808, 2000)
  (7808, 97)
  </code></pre>
  
  <p>does it only reduce the futre where every line has 1 or where every line has a 0 or how does it work?</p>