title: Pandas - Get value as frequency in groupby
body: <p>Can someone help me with the (possible) groupby in pandas.</p>
  
  <p>Here is the df:</p>
  
  <pre><code>    easy_donor  v_fam   count
  0   donor_1_NS  IGHV1   5202376
  1   donor_1_NS  IGHV2   1955547
  2   donor_1_NS  IGHV3   70426272
  3   donor_1_NS  IGHV4   452367
  4   donor_1_NS  IGHV5   4842145
  5   donor_1_NS  IGHV6   490142
  6   donor_1_NS  IGHV7   19708
  24  donor_2_NS  IGHV1   31258603
  25  donor_2_NS  IGHV2   5295899
  26  donor_2_NS  IGHV3   47286417
  27  donor_2_NS  IGHV4   44553802
  </code></pre>
  
  <p>Then I want each count as a frequency of the sum of the counts grouped by donor.</p>
  
  <p>Like:</p>
  
  <pre><code>df.groupby('easy_donor').sum()['count']
  easy_donor
  donor_1_NS     83394639
  donor_2_NS    129191591
  donor_3_HS    220549762
  donor_3_NS    104821016
  donor_4_HS    200444923
  donor_4_NS    121287306
  </code></pre>
  
  <p>Then each count in the original data frame divided by the groupby sum if they match the easy_donor column. Do I have to join on original dataframe?</p>