title: accumulate every value in last three cells in DataFrame in a faster way
body: <p>Suppose I have a Dataframe df_a:</p>
  <div class="s-table-container">
  <table class="s-table">
  <thead>
  <tr>
  <th>date</th>
  <th>a</th>
  <th>b</th>
  <th>c</th>
  </tr>
  </thead>
  <tbody>
  <tr>
  <td>2021-01-01</td>
  <td>10</td>
  <td>0</td>
  <td>10</td>
  </tr>
  <tr>
  <td>2021-01-02</td>
  <td>0</td>
  <td>0</td>
  <td>0</td>
  </tr>
  <tr>
  <td>2021-01-03</td>
  <td>5</td>
  <td>5</td>
  <td>0</td>
  </tr>
  <tr>
  <td>2021-01-04</td>
  <td>0</td>
  <td>0</td>
  <td>0</td>
  </tr>
  <tr>
  <td>2021-01-05</td>
  <td>0</td>
  <td>0</td>
  <td>0</td>
  </tr>
  <tr>
  <td>2021-01-06</td>
  <td>0</td>
  <td>0</td>
  <td>0</td>
  </tr>
  </tbody>
  </table>
  </div>
  <p>I want to accumulate every value in last three cells. For example the df_a will convert into df_b.</p>
  <div class="s-table-container">
  <table class="s-table">
  <thead>
  <tr>
  <th>date</th>
  <th>a</th>
  <th>b</th>
  <th>c</th>
  </tr>
  </thead>
  <tbody>
  <tr>
  <td>2021-01-01</td>
  <td>0</td>
  <td>0</td>
  <td>0</td>
  </tr>
  <tr>
  <td>2021-01-02</td>
  <td>10</td>
  <td>0</td>
  <td>10</td>
  </tr>
  <tr>
  <td>2021-01-03</td>
  <td>10</td>
  <td>0</td>
  <td>10</td>
  </tr>
  <tr>
  <td>2021-01-04</td>
  <td>15</td>
  <td>5</td>
  <td>10</td>
  </tr>
  <tr>
  <td>2021-01-05</td>
  <td>5</td>
  <td>5</td>
  <td>0</td>
  </tr>
  <tr>
  <td>2021-01-06</td>
  <td>5</td>
  <td>5</td>
  <td>0</td>
  </tr>
  </tbody>
  </table>
  </div>
  <p>Now I can use <code>for loop</code> but it is really slow. Is there any way to realize it fast?</p>