title: How do groupby elements in pandas based on consecutive row values
body: <p>I have a dataframe as below :</p>
  
  <pre><code>   distance_along_path
  0       0
  1       2.2
  2       4.5
  3       7.0
  4       0
  5       3.0
  6       5.0
  7       0
  8       2.0
  9       5.0
  10      7.0
  </code></pre>
  
  <p>I want be able to group these by the distance_along_path values, every time a 0 is seen a new group is created and until the next 0 all these rows are under 1 group as indicated below </p>
  
  <pre><code>   distance_along_path    group
  0       0                  A
  1       2.2                A
  2       4.5                A    
  3       7.0                A
  4       0                  B
  5       3.0                B
  6       5.0                B
  7       0                  C
  8       2.0                C
  9       5.0                C
  10      7.0                C
  </code></pre>
  
  <p>Thank you</p>