title: Summing multiple row values of various columns in Pandas
body: <p>I need to add row value of various columns and store it in same(or new) dataframe.
  eg:
  The dataframe looks something like this:</p>
  
  <pre><code>id  col1  col2  col3  col4 ...  col50
   1    1     12    3     44         0
   1    7      0    7      2         10
   1    2      3    0      4         9
   3    9      0    1      0         0
   3    1      1   11      1         0
  </code></pre>
  
  <p>And the expected values should be:</p>
  
  <pre><code>id  col1  col2  col3  col4...  col50
   1    10   15    10    46        19
   3    10    1    12     1         0
  </code></pre>
  
  <p>If I use <code>tmp2 = tmp2.iloc[:,1:50].sum()</code>, it changes the dimension of the dataframe. </p>