ValueError: The truth value of a DataFrame is ambiguous

Question

我有一个如下所示的数据框：

        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

我正在尝试添加一个新列，其中包含其中两列的百分比差异，但仅适用于 'downloaded' 中没有 0 的列。

我正在尝试为此使用如下函数：

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)

我收到一个错误：

---------------------------------------------------------------------------
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().

谁能帮我理解这个错误是什么意思？

此外，这是否是一个应用函数的好应用程序？我可以在申请中使用条件吗？在这种情况下我将如何使用它？

Answer 1

错误的原因是您试图按行进行（向量化计算），但实际上在您的函数中 diff() ratings[ratings.downloaded > 0] returns dataframe 和它前面的 if 是不明确的。错误消息反映了这一点。

您不妨回顾一下 Indexing and Selecting Data。下面的解决方案通过在开头设置它来设置默认值 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

Answer 2

Dataframe 对象不转换为布尔值，更改条件

if ratings[ratings.downloaded > 0]:

至

if len(ratings[ratings.downloaded > 0]) > 0:

ValueError: The truth value of a DataFrame is ambiguous

ValueError: The truth value of a DataFrame is ambiguous

python

python-3.x

pandas

valueerror