从Pandas DataFrame中选择列

Question

I am trying to select different columns and rows in dataframe Here are some examples

df1 = DataFrame(np.random.randn(6,4), index=list('abcdef'), columns=list('ABCD'))


    A   B   C   D
a   -0.767663    0.158213    0.502184    0.156238
b   -0.450274   -0.287952   -0.666661   -0.934083
c    2.142362   -1.212363    0.075363   -0.270905
d    0.075977    1.355053   -1.665973    1.266896
e   -1.251002    0.274878   -0.511252    1.734822
f   -0.587612    0.731301   -0.680246    0.286389

Example 1:

df1.loc[['a','b','d'],:]


       A                  B             C              D
a   -0.767663    0.158213    0.502184    0.156238
b   -0.450274   -0.287952   -0.666661   -0.934083
d    0.075977    1.355053   -1.665973    1.26689

Example2:

df1.loc[['a','b'],:'B']

A   B
a   -0.767663    0.158213
b   -0.450274   -0.2879520

Example3:

df1.loc['d':,'A':'C']
    A   B   C
d    0.075977    1.355053   -1.665973
e   -1.251002    0.274878   -0.511252
f   -0.587612    0.731301   -0.680246

Example4:

df1.loc[['d','e'],:'A']

    A
d    0.075977
e   -1.251002

Example5:

df1.loc[['a','d'],:['B','D']] ==> not a valid syntax

Error:IndexError: invalid slice

Any hints on how to select columns B and D for rows a and d

Answer 1

Just do this way :

df1.loc[['a','d'],['B','D']]

i:j means you want a slice from i to j (like in your example 3)

Here you don't want a slice so you don't need :