title: Downsampling a 2d numpy array in python
body: <p>I'm self learning python and have found a problem which requires down sampling a feature vector.  I need some help understanding how down-sampling a array. in the array each row represents an image by being number from <code>0</code> to <code>255</code>. I was wonder how you apply down-sampling to the array? I don't want to <code>scikit-learn</code> because I want to understand how to apply down-sampling.
  If you could explain down-sampling too that would be amazing thanks. </p>
  
  <p>the feature vector is 400x250</p>