No numeric types to aggregate for pandas

Question

I have pandas dataframe like this

df

id      channel           name      text
162928  p_total_2018     shintaro  myidid                
162929  Q_journey_2018   cna       mynamename
162930  p_fsdfad_2018    cna       mycomment   
.
.

Now I want to know how many variation of names are exist (in this case, there are two names shintaro, cna)

but

df.groupby('name').mean() shows the error No numeric types to aggregate

How can I get the rows of no dupulicate names??