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python - 在熊猫中应用功能

问题描述

当我运行以下

import pandas as pd


def my_func(E, I):

    return E * I


d = {'E': [1, 1], 'I': [2, 2]}
df = pd.DataFrame(data=d)
df['S'] = df.apply(lambda x: my_func(x['E'], x['I']),axis=1).map(lambda x: x[0])

我收到以下错误

Traceback (most recent call last):
  File "U:\GSY\scipt.py", line 14, in <module>
    df['S'] = df.apply(lambda x: my_func(x['E'], x['I']),axis=1).map(lambda x: x[0])
  File "C:\Users\gsy.LSH\AppData\Local\Packages\PythonSoftwareFoundation.Python.3.8_qbz5n2kfra8p0\LocalCache\local-packages\Python38\site-packages\pandas\core\series.py", line 3630, in map
    new_values = super()._map_values(arg, na_action=na_action)
  File "C:\Users\gsy.LSH\AppData\Local\Packages\PythonSoftwareFoundation.Python.3.8_qbz5n2kfra8p0\LocalCache\local-packages\Python38\site-packages\pandas\core\base.py", line 1145, in _map_values
    new_values = map_f(values, mapper)
  File "pandas\_libs\lib.pyx", line 2329, in pandas._libs.lib.map_infer
  File "U:\GSY\script.py", line 14, in <lambda>
    df['S'] = df.apply(lambda x: my_func(x['E'], x['I']),axis=1).map(lambda x: x[0])
TypeError: 'int' object is not subscriptable

我 100% 确定这在过去是有效的，因为我已经广泛使用它。有谁知道为什么会这样？

标签： pythonpandasapply

解决方案

只需将最后一张地图放在最后。该函数正在返回一个列表，而您的最后一个 map 函数正在尝试获取列表的第一个元素。

import pandas as pd

def my_func(E, I):
    return E * I

d = {'E': [1, 1], 'I': [2, 2]}
df = pd.DataFrame(data=d)
df['S'] = df.apply(lambda x: my_func(x['E'], x['I']),axis=1)

或者，但根据此处的评论，您可以将 my_func 中的值作为列表返回：

import pandas as pd

def my_func(E, I):
    return [E * I]

d = {'E': [1, 1], 'I': [2, 2]}
df = pd.DataFrame(data=d)
df['S'] = df.apply(lambda x: my_func(x['E'], x['I']),axis=1).map(lambda x: x[0])

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