系列的真值在数据框中不明确 [英] The truth value of a Series is ambiguous in dataframe

问题描述

我有相同的代码，我正在尝试通过简单的条件在pandas数据框中创建新字段:

I have the same code,I'm trying to create new field in pandas dataframe with simple conditions:

if df_reader['email1_b']=='NaN':
    df_reader['email1_fin']=df_reader['email1_a']
else:
    df_reader['email1_fin']=df_reader['email1_b']

但是我看到这个奇怪的错误:

ValueError                                Traceback (most recent call last)
<ipython-input-92-46d604271768> in <module>()
----> 1 if df_reader['email1_b']=='NaN':
      2     df_reader['email1_fin']=df_reader['email1_a']
      3 else:
      4     df_reader['email1_fin']=df_reader['email1_b']

/home/user/GL-env_py-gcc4.8.5/lib/python2.7/site-packages/pandas/core/generic.pyc in __nonzero__(self)
    953         raise ValueError("The truth value of a {0} is ambiguous. "
    954                          "Use a.empty, a.bool(), a.item(), a.any() or a.all()."
--> 955                          .format(self.__class__.__name__))
    956 
    957     __bool__ = __nonzero__

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

有人可以向我解释一下，我需要做什么吗?

Can anybody explain me, what I need to with this?

推荐答案

df_reader['email1_b']=='NaN'是布尔值的向量(每行一个)，但是您需要一个布尔值才能使if起作用.改用它:

df_reader['email1_b']=='NaN' is a vector of Boolean values (one per row), but you need one Boolean value for if to work. Use this instead:

df_reader['email1_fin'] = np.where(df_reader['email1_b']=='NaN', 
                                   df_reader['email1_a'],
                                   df_reader['email1_b'])

作为旁注，您确定关于'NaN'吗?不是NaN吗?在后一种情况下，您的表达式应为:

As a side note, are you sure about 'NaN'? Is it not NaN? In the latter case, your expression should be:

df_reader['email1_fin'] = np.where(df_reader['email1_b'].isnull(), 
                                   df_reader['email1_a'],
                                   df_reader['email1_b'])

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