title: how PCA fit transform on test set
body: <p>I am using the <code>from sklearn.decomposition import PCA library, IncrementalPCA</code> to reduce the dimensionality of my problem as follows:</p>
  
  <pre><code>training_data = [...] 
  training_target = [...]
  test_data = [...]
  test_target = [...] 
  ipca = IncrementalPCA(n_components, batch_size)
  new_training_data = ipca.fit_transform(training_data)
  </code></pre>
  
  <p>To run the tests with a given classifier, I need to fit the test set with the information obtained in the training set (something like eigenvalues and eigenvectors), to reduce the same size of the new training set. But how can I do this with this library (or some other), since the <code>ipca.fit_transform(data)</code> does not return anything to me like eg eigpairs or some value to resize the dimension of the test set?</p>