title: Calculate the sum of the row values in a new dataframe
body: <p>I have this type of dataframe which represents the label given by each annotator (column name) for a mention in a text (index):</p>
  <p><a href="https://i.stack.imgur.com/9Y4vh.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/9Y4vh.png" alt="enter image description here" /></a></p>
  <p>My goal is to transform this view, to get the sum of the annotators for a label given at each mention of the text, as:</p>
  <p><a href="https://i.stack.imgur.com/LwDr3.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/LwDr3.png" alt="enter image description here" /></a></p>
  <p>Will anyone have a lead for doing this? thanks in advance.</p>