title: Fill missing Values by a ratio of other values in Pandas
body: <p>I have a column in a Dataframe in Pandas with around 78% missing values.</p>
  
  <p>The remaining 22% values are divided between three labels - SC, ST, GEN with the following ratios.</p>
  
  <p>SC - 16%
  ST - 8%
  GEN - 76%</p>
  
  <p>I need to replace the missing values by the above three values so that the ratio of all the elements remains same as above. The assignment can be random as long the the ratio remains as above.</p>
  
  <p>How do I accomplish this?</p>