title: Calculate percentage on DataFrame
body: <p>I'm trying to calculate the percentage of each crime of the following Dataframe:</p>
  
  <pre><code>        Violent     Murder      Larceny_Theft   Vehicle_Theft
  Year
  1960    288460      3095700     1855400         328200
  1961    289390      3198600     1913000         336000
  1962    301510      3450700     2089600         366800
  1963    316970      3792500     2297800         408300
  1964    364220      4200400     2514400         472800
  </code></pre>
  
  <p>So I should calculate first the total of crimes per year and then use that to calculate the percentage of each crime. I was trying the following:</p>
  
  <pre><code>&gt; perc = (crime *100) / crime.sum(axis=1)
  </code></pre>
  
  <p>Any thoughts?
  Thank you!</p>