title: Pandas, merging two rows with different index names
body: <p>I have data frame, <code>df</code>, that looks like this:</p>
  
  <pre><code>              Done  Todo  Total                     
  Painting       55    54    109
  Fitting        17    26     43
  Plumbing       10    26     36
  Electricity     7    29     36
  Piping         29     5     34
  Roofing        12    20     32
  </code></pre>
  
  <p>I need to merge indexes 'Plumbing' and 'Piping' so that I have a data frame that looks like this:</p>
  
  <pre><code>              Done  Todo  Total                     
  Painting       55    54    109
  Fitting        17    26     43
  Plumbing       39    46     68
  Electricity     7    29     36
  Piping         29     5     34
  </code></pre>
  
  <p>How can I achieve this is pandas?</p>
  
  <p>I have tried the following</p>
  
  <pre><code>df.loc['Plumbing'] = df.loc['Plumbing'] + df.loc['Piping']
  </code></pre>
  
  <p>but this keeps the 'Piping' row in the data frame. Is there a way of doing it automatically so that the 'Piping row is automatically removed?
  <a href="https://stackoverflow.com/questions/17438906/combining-rows-in-pandas">This</a> and <a href="https://stackoverflow.com/questions/16684346/pandas-group-by-operations-on-a-data-frame">this</a> questions did not provide what I need.</p>