pandas 系列的真值在数据框中不明确
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The truth value of a Series is ambiguous in dataframe
提问by DYZ
I have the same code,I'm trying to create new field in pandas dataframe with simple conditions:
我有相同的代码，我正在尝试使用简单的条件在 Pandas 数据框中创建新字段：
if df_reader['email1_b']=='NaN':
df_reader['email1_fin']=df_reader['email1_a']
else:
df_reader['email1_fin']=df_reader['email1_b']
But I see this strange mistake:
但我看到了这个奇怪的错误：
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().
Can anybody explain me, what I need to with this?
任何人都可以解释我，我需要什么？
回答by DYZ
df_reader['email1_b']=='NaN'is a vector of Boolean values (one per row), but you need one Boolean value for ifto work. Use this instead:
df_reader['email1_b']=='NaN'是一个布尔值向量（每行一个），但您需要一个布尔值if才能工作。改用这个：
df_reader['email1_fin'] = np.where(df_reader['email1_b']=='NaN',
df_reader['email1_a'],
df_reader['email1_b'])
As a side note, are you sure about 'NaN'? Is it not NaN? In the latter case, your expression should be:
作为旁注，您确定'NaN'吗？不是NaN吗？在后一种情况下，您的表达式应该是：
df_reader['email1_fin'] = np.where(df_reader['email1_b'].isnull(),
df_reader['email1_a'],
df_reader['email1_b'])
回答by EdChum
ifexpects a scalar value to be returned, it doesn't understand an array of booleans which is what is returned by your conditions. If you think about it what should it do if a single value in this array is False/True?
if期望返回一个标量值，它不理解布尔数组，这是您的条件返回的内容。如果您考虑一下，如果此数组中的单个值是False/ 该True怎么办？
to do this properly you can do the following:
要正确执行此操作，您可以执行以下操作：
df_reader['email1_fin'] = np.where(df_reader['email1_b'] == 'NaN', df_reader['email1_a'], df_reader['email1_b'] )
also you seem to be comparing against the str'NaN'rather than the numerical NaNis this intended?
您似乎也是在比较str'NaN'而不是数字NaN，这是打算吗？
