title: two-level indexing in dataframes in pandas : count the number of second level index for each first level index
body: <p>I have a dataframe pasted below with two-level indexing (first level is statename and second level is county name): 
  <a href="https://i.stack.imgur.com/KDwZf.png" rel="nofollow noreferrer">the image contains the statename and the counties in it in the second column</a></p>
  
  <p>I need to count the number of counties in each state. (In the image pasted i have just information for a single state but the entire dataframe consists of several such similar entries for states and corresponding county names.) 
  for ex. in the above pic it should return 5 for Alabama (i know there are 60 other counties within alabama but i have just pasted a small part of the bigger dataframe). 
  Which pandas function can be used to return the counties count for each state?
  I am a novice to pandas and just in the learning stage. </p>
  
  <p>thanks for the help in advance.</p>