title: Plotting correlation heatmaps with Seaborn FacetGrid
body: <p>I am trying to create a single image with heatmaps representing the correlation of features of data points for each label separately. With seaborn I can create a heatmap for a single class like so</p>
  
  <pre><code>grouped = df.groupby('target')
  sns.heatmap(grouped.get_group('Class_1').corr())
  </code></pre>
  
  <p>An I get this which makes sense:</p>
  
  <p><img src="https://i.stack.imgur.com/YX0Ik.png" alt="Class_1 correlation heatmap"></p>
  
  <p>But then I try to make a list of all the labels like so:</p>
  
  <pre><code>g = sns.FacetGrid(df, col='target')
  g.map(lambda grp: sns.heatmap(grp.corr()))
  </code></pre>
  
  <p>And sadly I get this which makes no sense to me:</p>
  
  <p><img src="https://i.stack.imgur.com/OvWVI.png" alt="Failing attempt to plot all classes"></p>