what is different between groupby.first, groupby.nth, groupby.head when as_index=False

Question

Edit: the rookie mistake I made in string np.nan having pointed out by @coldspeed, @wen-ben, @ALollz. Answers are quite good, so I don\'t d

Answer 1

Here is the different, you need to make the np.nan to NaN , in your original df it is string , after convert it , you will see the different

df=df.mask(df=='np.nan')
df.groupby('A', as_index=False).head(1) #df.groupby('A', as_index=False).nth(0)

Out[8]: 
   A    B
0  1  NaN
3  2    8
df.groupby('A', as_index=False).first() 
# the reason why first have the index reset, 
#since it will have chance select the value from different row within the group, 
#when the first item is NaN it will skip it to find the first not null value 
#rather than from the same row, 
#If still keep the original row index will be misleading. 
Out[9]: 
   A  B
0  1  4
1  2  8