title: Get count unique values in a row in pandas
body: <p>Suppose I have the following data frame:</p>
  
  <pre><code>0     1        2
  new   NaN      NaN
  new   one      one
  a     b        c
  NaN   NaN      NaN
  </code></pre>
  
  <p>How would I get the number of unique (non-NaN) values in a row, such as:</p>
  
  <pre><code>0     1        2       _num_unique_values
  new   NaN      NaN     1
  new   one      one     2
  a     b        c       3
  NaN   NaN      NaN     0
  </code></pre>
  
  <p>I suppose it would be something along the lines of:</p>
  
  <pre><code>df['_num_unique_values'] = len(set(df.loc.tolist())) ??
  </code></pre>