df=pd.DataFrame([["casy","Nice picture!"],
["linda","I like this "],
["casy ","Nice picture! "],
["tom ","I disagree "],
["bob ","Follow me "],
["bob ","Follow me "],
["bob ","Follow me "],
["bob ","Follow me "],
["casy ","Nice picture! "],
["casy ","Wow! "],
["linda ","Interesting post "],
["linda","Check my profile"],
["bob ","Dissapointing"],
["casy ","Wow! "]
                ] ,columns=["Author","Comment"])


df

Author	Comment
0	casy	Nice picture!
1	linda	I like this
2	casy	Nice picture!
3	tom	I disagree
4	bob	Follow me
5	bob	Follow me
6	bob	Follow me
7	bob	Follow me
8	casy	Nice picture!
9	casy	Wow!
10	linda	Interesting post
11	linda	Check my profile
12	bob	Dissapointing
13	casy	Wow!

df_sorted = (df.groupby(['Author', 'Comment'], sort=False).size()
       .sort_values(ascending=False)
       .reset_index(name='Number')
       .reindex(columns=['Author','Number','Comment']))
df_sorted


Author	Number	Comment
0	bob	4	Follow me
1	casy	2	Wow!
2	casy	2	Nice picture!
3	bob	1	Dissapointing
4	linda	1	Check my profile
5	linda	1	Interesting post
6	tom	1	I disagree
7	linda	1	I like this
8	casy	1	Nice picture!