title: Group pandas dataframe values by ID and map the operations on values ( assign single workers per ID)
body: <p>I have a large DataFrame and I want to map operations on groups of values to speed it up.</p>
  
  <p>Currently I use Transform(). This is how I would do it for a small DataFrame.</p>
  
  <pre><code>df =pd.DataFrame({'ID':[1,1,2,2,3,3], 'Value':[.1,.4,.5,.9,.1,.3]})
  def myfunc(x):
      return x/x.sum()
  df.groupby('ID').transform(myfunc)
  </code></pre>
  
  <p>I want to map the operations so it is done in parallel per IDs. Thank you in advance.</p>