title: Why does this scatter plot only plot one point?
body: <p>I am following the tutorial <a href="https://github.com/ogrisel/parallel_ml_tutorial/blob/master/rendered_notebooks/07%20-%20Text%20Feature%20Extraction%20for%20Classification%20and%20Clustering.ipynb" rel="nofollow">here</a> to classify documents. I am having a problem with this block of code:</p>
  
  <pre><code>from itertools import cycle
  
  colors = ['b', 'g', 'r', 'c', 'm', 'y', 'k']
  for i, c in zip(np.unique(y_train), cycle(colors)):
      plt.scatter(X_train_small_pca[y_train == i, 0],
                 X_train_small_pca[y_train == i, 1],
                 c=c, label=twenty_train_small.target_names[i], alpha=0.5)
  
  _ = plt.legend(loc='best')
  </code></pre>
  
  <p>I am expecting a scatter plot similar to the example in the tutorial with a lot of date points. Instead, I receive one data point.</p>
  
  <p>My <code>X_train_small_pca</code> looks like this:</p>
  
  <pre><code>array([[ 0.3310974 , -0.07091423],
         [ 0.39871607, -0.26434965],
         [ 0.47174667, -0.22348895],
         ..., 
         [ 0.49631973,  0.12411882],
         [ 0.36678049,  0.24062078],
         [ 0.22540712, -0.1105503 ]])
  </code></pre>
  
  <p>The <code>zip</code> line produces this, which is iterated through:</p>
  
  <pre><code>[(u'alt.atheism', 'b'),
   (u'talk.religion.misc', 'g'),
   (u'comp.graphics', 'r'),
   (u'sci.space', 'c')]
  </code></pre>
  
  <p>Finally, I put a <code>print</code> line immediately after the <code>for</code> loop begins, and I get this output:</p>
  
  <pre><code>(u'alt.atheism', 0.33109737451727428, -0.070908715239074438)
  (u'talk.religion.misc', 0.33109737451727428, -0.070908715239074438)
  (u'comp.graphics', 0.33109737451727428, -0.070908715239074438)
  (u'sci.space', 0.33109737451727428, -0.070908715239074438)
  </code></pre>
  
  <p>Why is my scatter plot only seeing the single point for all categories and why is it only seeing 4 total lines, instead of all of my <code>X_train_small_pca</code>, which is the expected size?</p>