title: create a dataframe from a list of length-unequal lists
body: <p>I try to convert such a list:</p>
  
  <pre><code>l = [[1, 2, 3, 17], [4, 19], [5]]
  </code></pre>
  
  <p>to a dataframe having each of the number as indice, and position of list as value.</p>
  
  <p>For example, 19 is in the second list, I thus expect to get somwhere one row with "19" as index and "1" as value, and so on.</p>
  
  <p>I managed to get it (cf.boiler plate below), but I guess there is something more simple  </p>
  
  <pre><code>&gt;&gt;&gt; df=pd.DataFrame(l)    
  &gt;&gt;&gt; df=df.unstack().reset_index(level=0,drop=True)    
  &gt;&gt;&gt; df=df[df.notnull()==True]   # remove NaN rows 
  &gt;&gt;&gt; df=pd.DataFrame(df)    
  &gt;&gt;&gt; df = df.reset_index().set_index(0)    
  &gt;&gt;&gt; print df
      index
  0        
  1       0
  4       1
  5       2
  2       0
  19      1
  3       0
  17      0
  </code></pre>
  
  <p>Thanks in advance.</p>