How can I extract the first and last rows of a given dataframe as a new dataframe in pandas?
I've tried to use iloc to select the desired rows and then concat as in:
df=pd.DataFrame({'a':range(1,5), 'b':['a','b','c','d']})
pd.concat([df.iloc[0,:], df.iloc[-1,:]])
but this does not produce a pandas dataframe:
a 1
b a
a 4
b d
dtype: object
Some of the other answers duplicate the first row if the frame only contains a single row. If that's a concern
df[0::len(df)-1 if len(df) > 1 else 1]
works even for single row-dataframes.
Example: For the following dataframe this will not create a duplicate:
df = pd.DataFrame({'a': [1], 'b':['a']})
df2 = df[0::len(df)-1 if len(df) > 1 else 1]
print df2
a b
0 1 a
whereas this does:
df3 = df.iloc[[0, -1]]
print df3
a b
0 1 a
0 1 a
because the single row is the first AND last row at the same time.