title: Pandas DataFrame Groupby two columns and get counts
body: <p>I have a pandas dataframe in the following format:</p>
  
  <pre><code>df = pd.DataFrame([[1.1, 1.1, 1.1, 2.6, 2.5, 3.4,2.6,2.6,3.4,3.4,2.6,1.1,1.1,3.3], list('AAABBBBABCBDDD'), [1.1, 1.7, 2.5, 2.6, 3.3, 3.8,4.0,4.2,4.3,4.5,4.6,4.7,4.7,4.8], ['x/y/z','x/y','x/y/z/n','x/u','x','x/u/v','x/y/z','x','x/u/v/b','-','x/y','x/y/z','x','x/u/v/w'],['1','3','3','2','4','2','5','3','6','3','5','1','1','1']]).T
  df.columns = ['col1','col2','col3','col4','col5']
  </code></pre>
  
  <p>df:</p>
  
  <pre><code>   col1 col2 col3     col4 col5
  0   1.1    A  1.1    x/y/z    1
  1   1.1    A  1.7      x/y    3
  2   1.1    A  2.5  x/y/z/n    3
  3   2.6    B  2.6      x/u    2
  4   2.5    B  3.3        x    4
  5   3.4    B  3.8    x/u/v    2
  6   2.6    B    4    x/y/z    5
  7   2.6    A  4.2        x    3
  8   3.4    B  4.3  x/u/v/b    6
  9   3.4    C  4.5        -    3
  10  2.6    B  4.6      x/y    5
  11  1.1    D  4.7    x/y/z    1
  12  1.1    D  4.7        x    1
  13  3.3    D  4.8  x/u/v/w    1
  </code></pre>
  
  <p>Now I want to group this by two columns like following:</p>
  
  <pre><code>df.groupby(['col5','col2']).reset_index()
  </code></pre>
  
  <p>OutPut:</p>
  
  <pre><code>             index col1 col2 col3     col4 col5
  col5 col2                                      
  1    A    0      0  1.1    A  1.1    x/y/z    1
       D    0     11  1.1    D  4.7    x/y/z    1
            1     12  1.1    D  4.7        x    1
            2     13  3.3    D  4.8  x/u/v/w    1
  2    B    0      3  2.6    B  2.6      x/u    2
            1      5  3.4    B  3.8    x/u/v    2
  3    A    0      1  1.1    A  1.7      x/y    3
            1      2  1.1    A  2.5  x/y/z/n    3
            2      7  2.6    A  4.2        x    3
       C    0      9  3.4    C  4.5        -    3
  4    B    0      4  2.5    B  3.3        x    4
  5    B    0      6  2.6    B    4    x/y/z    5
            1     10  2.6    B  4.6      x/y    5
  6    B    0      8  3.4    B  4.3  x/u/v/b    6
  </code></pre>
  
  <p>I want to get the count by each row like following.
  Expected Output:</p>
  
  <pre><code>col5 col2 count
  1    A      1
       D      3
  2    B      2
  etc...
  </code></pre>
  
  <p>How to get my expected output? And I want to find largest count for each 'col2' value?</p>