应用方法的问题

Question

def mean1(x):
return sum(x)/len(x)
df2['children'] = df2['children'].apply(mean1)

我得到的错误如下：-'t'对象不可迭代

我认为我正确地应用了Apply((函数。但仍然出现错误。

Answer 1

您应该在列上应用mean1，而不是项：

df2['children'] = mean1(df2['children'])

或者更好，使用熊猫内置的mean方法：

df2['children'] = df2['children'].mean()

Answer 2

使用示例数据帧

In [372]: df
Out[372]: 
0    1   2   3
1  0    1   2   3
2  4  100   6   7
3  8    9  10  11
In [373]: df[1]     # one column
Out[373]: 
1      1
2    100
3      9
Name: 1, dtype: int64

和你的函数-修改以显示它得到了什么x：

In [375]: def mean1(x):
...:     print(x)
...:     return sum(x)/len(x)
...: 
In [376]: df[1].apply(mean1)
1
Traceback (most recent call last):
File "<ipython-input-376-e12f9dfea5ae>", line 1, in <module>
df[1].apply(mean1)
File "/usr/local/lib/python3.8/dist-packages/pandas/core/series.py", line 4357, in apply
return SeriesApply(self, func, convert_dtype, args, kwargs).apply()
File "/usr/local/lib/python3.8/dist-packages/pandas/core/apply.py", line 1043, in apply
return self.apply_standard()
File "/usr/local/lib/python3.8/dist-packages/pandas/core/apply.py", line 1099, in apply_standard
mapped = lib.map_infer(
File "pandas/_libs/lib.pyx", line 2859, in pandas._libs.lib.map_infer
File "<ipython-input-375-48efb527b53e>", line 3, in mean1
return sum(x)/len(x)
TypeError: 'int' object is not iterable

参见x就是1，一个单独的数字。Python不能在1上执行sum和len。错误不在apply中，而是在您的函数中，该函数没有考虑单个数字。

你打算做什么？取整列的平均值？或者每个单元格中数组或列表的平均值？

In [378]: mean1(df[1])
1      1
2    100
3      9
Name: 1, dtype: int64
Out[378]: 36.666666666666664

如果数据帧列包含列表或数组，apply和您的函数就会工作

In [386]: df = pd.DataFrame([None,None,None],columns=['one'])
In [387]: df['one'] = [np.ones(5).tolist(),np.arange(4).tolist(),np.zeros(9).tol
...: ist()]
In [388]: df
Out[388]: 
one
0                      [1.0, 1.0, 1.0, 1.0, 1.0]
1                                   [0, 1, 2, 3]
2  [0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0]
In [389]: df['one'].apply(mean1)
[1.0, 1.0, 1.0, 1.0, 1.0]
[0, 1, 2, 3]
[0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0]
Out[389]: 
0    1.0
1    1.5
2    0.0
Name: one, dtype: float64