[英]dataframe: ValueError: The truth value of a Series is ambiguous
[英]ValueError: The truth value of a DataFrame is ambiguous
我有一個看起來像這樣的數據框:
total downloaded avg_rating
id
1 2 2 5.0
2 12 12 4.5
3 1 1 5.0
4 1 1 4.0
5 0 0 0.0
我正在嘗試添加一個新列,其中兩個列的百分比差異,但僅適用於“已下載”中沒有 0 的列。
我正在嘗試為此使用一個函數,如下所示:
def diff(ratings):
if ratings[ratings.downloaded > 0]:
val = (ratings['total'] - ratings['downloaded']) / ratings['downloaded']
else:
val = 0
return val
ratings['Pct Diff'] = diff(ratings)
我收到一個錯誤:
---------------------------------------------------------------------------
ValueError Traceback (most recent call last)
<ipython-input-129-729c09bf14e8> in <module>()
6 return val
7
----> 8 ratings['Pct Diff'] = diff(ratings)
<ipython-input-129-729c09bf14e8> in diff(ratings)
1 def diff(ratings):
----> 2 if ratings[ratings.downloaded > 0]:
3 val = (ratings['total'] - ratings['downloaded']) /
ratings['downloaded']
4 else:
5 val = 0
~\Anaconda3\lib\site-packages\pandas\core\generic.py 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 DataFrame is ambiguous. Use a.empty, a.bool(), a.item(), a.any() or a.all().
有人可以幫我理解這個錯誤是什么意思嗎?
另外,這是否是應用功能的好應用? 我可以在申請中使用條件嗎? 在這種情況下我將如何使用它?
出現錯誤的原因是您正在嘗試按行進行(向量化計算),但實際上在您的函數diff()
ratings[ratings.downloaded > 0]
返回數據幀的一個子集,並在它前面加上if
是不明確的. 錯誤消息反映了這一點。
您可能希望查看索引和選擇數據。 下面的解決方案通過在開始時設置它來設置默認值 0。
import pandas as pd
df = pd.DataFrame([[2, 2, 5.0], [12, 12, 4.5], [10, 5, 3.0],
[20, 2, 3.5], [3, 0, 0.0], [0, 0, 0.0]],
columns=['total', 'downloaded', 'avg_rating'])
df['Pct Diff'] = 0
df.loc[df['downloaded'] > 0, 'Pct Diff'] = (df['total'] - df['downloaded']) / df['total']
# total downloaded avg_rating Pct Diff
# 0 2 2 5.0 0.0
# 1 12 12 4.5 0.0
# 2 10 5 3.0 0.5
# 3 20 2 3.5 0.9
# 4 3 0 0.0 0.0
# 5 0 0 0.0 0.0
數據框對象不轉換為布爾值,更改條件
if ratings[ratings.downloaded > 0]:
到
if len(ratings[ratings.downloaded > 0]) > 0:
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