ValueError:系列的真值是不明确的。使用a.empty、a.bool()、a.item()、a.any()或a.all()。df[condition]

Question

如果列“embark_town”中的数据是“南安普敦”，我想将它们全部改为“曼彻斯特”。因此，在使用条件设置访问数据之后，我应用了'apply‘函数。有什么问题吗？

# Import Packages
import pandas as pd 
import numpy as np
import seaborn as sns

# dataset upload
df = sns.load_dataset("titanic")
df = df.rename(columns={'pclass':'passenger_class','sex':'gender','age':'old'})

def change(name):
  if name == 'Southampton':
    name = 'Manchester'
  return name

condition = (df.embark_town == 'Southampton')

df[condition] = df[condition].apply(change)
df

得到一个错误：

---------------------------------------------------------------------------
ValueError                                Traceback (most recent call last)
<ipython-input-7-2cf6d75dce9e> in <module>()
     14 
     15 condition = (df.embark_town == 'Southampton')
---> 16 df[condition] = df[condition].apply(change)
     17 df
     18 # df['embark_town'] = df['embark_town'].apply(change)

5 frames
/usr/local/lib/python3.7/dist-packages/pandas/core/generic.py in __nonzero__(self)
   1328     def __nonzero__(self):
   1329         raise ValueError(
-> 1330             f"The truth value of a {type(self).__name__} is ambiguous. "
   1331             "Use a.empty, a.bool(), a.item(), a.any() or a.all()."
   1332         )

ValueError: The truth value of a Series is ambiguous. Use a.empty, a.bool(), a.item(), a.any() or a.all().

Answer 1

正如在评论中所指出的。DataFrame.apply使用Series作为输入。定义的change(name)函数需要一个字符串。消息ValueError: The truth value of a Series is ambiguous. Use a.empty, a.bool(), a.item(), a.any() or a.all().来自试图将Series与字符串进行比较。

Register指出的一个修复方法是使用条件。

condition = (df[‘embark_town’] == 'Southampton')
df[condition]['embark_town'] = 'Manchester'

要继续使用apply，更改函数需要如下所示：

def change(series):
  if series.name == 'embark_town':
      series[series.values == 'Southampton'] = 'Manchester'

  return series