title: nested dictionary based on 3 dataframe columns
body: <p>im trying to build a nested dictionary based on 3 pandas df columns:</p>
  
  <p>dataframe: stops
  columns: 'direction' (1-2) ,'stop_num'(1-23 if the direction is 1 and 100-2300 if direction is 2),'name_eng'</p>
  
  <p>what i was trying to do is:</p>
  
  <p>dct = {x: {y:z} for x, y, z in zip(stops['direction'],stops['name_eng'],stops['stop_num'])}</p>
  
  <p>the result i get is a nested dictionary indeed but for unknown reason i get only the last value in y:z so the dictionary look like:</p>
  
  <p>{1:{1:'aaa'},'2:{100:'bbb'}}</p>
  
  <p>any idea what am i doing wrong? 
  what i need is a nested dictionary with two dictionaries for each direction.</p>
  
  <p>thanks!</p>