title: what is the difference between 'transform' and 'fit_transform' in sklearn
body: <p>In the sklearn-python toolbox, there are two functions <code>transform</code> and <code>fit_transform</code> about <code>sklearn.decomposition.RandomizedPCA</code>. The description of two functions are as follows </p>
  
  <p><img src="https://i.stack.imgur.com/Oy8kD.png" alt="enter image description here">
  <img src="https://i.stack.imgur.com/JpZk6.png" alt="enter image description here"></p>
  
  <p>But what is the difference between them ? </p>