When slicing a 1 row pandas dataframe the slice becomes a series

问题

Why when I slice a pandas dataframe containing only 1 row, the slice becomes a pandas series? How can I keep it a dataframe?

df=pd.DataFrame(data=[[1,2,3]],columns=['a','b','c'])
df
Out[37]: 
   a  b  c
0  1  2  3


a=df.iloc[0]

a
Out[39]: 
a    1
b    2
c    3
Name: 0, dtype: int64

回答1:

To avoid the intermediate step of re-converting back to a DataFrame, use double brackets when indexing:

a = df.iloc[[0]]
print(a)
   a  b  c
0  1  2  3

Speed:

%timeit df.iloc[[0]]
192 µs per loop

%timeit df.loc[0].to_frame().T
468 µs per loop

回答2:

Use to_frame() and T to transpose:

df.loc[0].to_frame()

   0
a  1
b  2
c  3

and

df.loc[0].to_frame().T

   a  b  c
0  1  2  3

OR

Option #2 use double brackets [[]]

df.iloc[[0]]

   a  b  c
0  1  2  3

回答3:

Or you can slice by index

a=df.iloc[df.index==0]

a
Out[1782]: 
   a  b  c
0  1  2  3

来源：https://stackoverflow.com/questions/45818612/when-slicing-a-1-row-pandas-dataframe-the-slice-becomes-a-series