向pandas DataFrame添加具有列平均值的行

Question

我有一个由一些传感器读数组成的熊猫DataFrame，如下所示：

       diode1  diode2  diode3  diode4
Time
0.530       7       0      10      16
1.218      17       7      14      19
1.895      13       8      16      17
2.570       8       2      16      17
3.240      14       8      17      19
3.910      13       6      17      18
4.594      13       5      16      19
5.265       9       0      12      16
5.948      12       3      16      17
6.632      10       2      15      17

我已经编写了代码，用每列的均值添加另一行：

# List of the averages for the test. 
averages = [df[key].describe()['mean'] for key in df]
indexes = df.index.tolist()
indexes.append('mean')
df.reindex(indexes)
# Adding the mean row to the bottom of the DataFrame

i = 0
for key in df:
    df.set_value('mean', key, averages[i])
    i += 1

这样就得到了我想要的结果，即如下所示的DataFrame：

       diode1  diode2  diode3  diode4
Time
0.53      7.0     0.0    10.0    16.0
1.218    17.0     7.0    14.0    19.0
1.895    13.0     8.0    16.0    17.0
2.57      8.0     2.0    16.0    17.0
3.24     14.0     8.0    17.0    19.0
3.91     13.0     6.0    17.0    18.0
4.594    13.0     5.0    16.0    19.0
5.265     9.0     0.0    12.0    16.0
5.948    12.0     3.0    16.0    17.0
6.632    10.0     2.0    15.0    17.0
mean     11.6     4.1    14.9    17.5

但是，我确信这不是添加行的最有效方式。我曾尝试使用append with the means saved as a pandas Series，但最终得到的结果如下：

    diode1  diode2  diode3  diode4                     mean
0      7.0     0.0    10.0    14.0                      NaN
1      9.0     0.0    10.0    15.0                      NaN
2     10.0     5.0    14.0    20.0                      NaN
3      6.0     0.0     7.0    14.0                      NaN
4      7.0     0.0    10.0    15.0                      NaN
5      7.0     0.0     8.0    14.0                      NaN
6      7.0     0.0    11.0    14.0                      NaN
7      7.0     0.0     2.0    11.0                      NaN
8      2.0     0.0     4.0    12.0                      NaN
9      4.0     0.0     0.0     6.0                      NaN
10     NaN     NaN     NaN     NaN  [11.6, 4.1, 14.9, 17.5]

我想知道是否有更有效的方法将索引为“mean”的行和每列的平均值添加到熊猫DataFrame的底部。

Answer 1

为setting with enlargement使用loc

df.loc['mean'] = df.mean()

结果输出：

       diode1  diode2  diode3  diode4
Time                                 
0.53      7.0     0.0    10.0    16.0
1.218    17.0     7.0    14.0    19.0
1.895    13.0     8.0    16.0    17.0
2.57      8.0     2.0    16.0    17.0
3.24     14.0     8.0    17.0    19.0
3.91     13.0     6.0    17.0    18.0
4.594    13.0     5.0    16.0    19.0
5.265     9.0     0.0    12.0    16.0
5.948    12.0     3.0    16.0    17.0
6.632    10.0     2.0    15.0    17.0
mean     11.6     4.1    14.9    17.5