使用逻辑表达式和if语句评估pandas系列值 [英] Evaluating pandas series values with logical expressions and if-statements

问题描述

我无法使用if语句评估字典中的值。

I'm having trouble evaluating values from a dictionary using if statements.

给定以下字典，我从数据框导入（如果重要）：

Given the following dictionary, which I imported from a dataframe (in case it matters):

>>> pnl[company]
29:   Active Credit       Date   Debit Strike Type
0      1      0 2013-01-08  2.3265  21.15  Put
1      0      0 2012-11-26      40     80  Put
2      0      0 2012-11-26     400     80  Put

我试图评估以下声明以建立最后一个值的值有效：

I tried to evaluate the following statment to establish the value of the last value of Active:

if pnl[company].tail(1)['Active']==1:
    print 'yay'

但是，我遇到以下错误消息：

However,I was confronted by the following error message:

Traceback (most recent call last):
  File "<pyshell#69>", line 1, in <module>
    if pnl[company].tail(1)['Active']==1:
  File "/usr/lib/python2.7/dist-packages/pandas/core/generic.py", line 676, in __nonzero__
    .format(self.__class__.__name__))
ValueError: The truth value of a Series is ambiguous. Use a.empty, a.bool(), a.item(), a.any() or a.all().

这令我感到惊讶，因为我可以使用上面的命令显示我想要的值而没有if语句：

This surprised me, given that I could display the value I wanted using the above command without the if statement:

>>> pnl[company].tail(1)['Active']
30: 2    0
Name: Active, dtype: object

鉴于该值明显为零且索引为2，我尝试了以下内容进行简短的健全性检查，发现事情没有像我预期的那样发生：

Given that the value is clearly zero and the index is 2, I tried the following for a brief sanity check and found that things weren't happening as I might have expected:

>>> if pnl[company]['Active'][2]==0:
...     print 'woo-hoo'
... else:
...     print 'doh'


doh

我的问题是：

1）这里可能会发生什么？我怀疑我在一些基本层面上误解了字典。

1) What might be going on here? I suspect I'm misunderstanding dictionaries on some fundamental level.

2）我注意到，当我调出这个字典的任何给定值时，左边的数字增加了1.这代表什么？例如：

2) I noticed that as I bring up any given value of this dictionary, the number on the left increases by 1. What does this represent? For example:

>>> pnl[company].tail(1)['Active']
31: 2    0
Name: Active, dtype: object
>>> pnl[company].tail(1)['Active']
32: 2    0
Name: Active, dtype: object
>>> pnl[company].tail(1)['Active']
33: 2    0
Name: Active, dtype: object
>>> pnl[company].tail(1)['Active']
34: 2    0
Name: Active, dtype: object

提前感谢您提供任何帮助。

Thanks in advance for any help.

推荐答案

您的收益是熊猫系列对象并不能以您尝试的方式进行评估，即使它只是您需要将行更改为的单个值：

What you yield is a Pandas Series object and this cannot be evaluated in the manner you are attempting even though it is just a single value you need to change your line to:

if pnl[company].tail(1)['Active'].any()==1:
  print 'yay'

关于第二个问题，请参阅我的评论。

With respect to your second question see my comment.

编辑

从评论和链接到你的输出，调用 any（）修复了错误信息，但你的数据实际上是字符串所以比较仍然失败，您可以这样做：

From the comments and link to your output, calling any() fixed the error message but your data is actually strings so the comparison still failed, you could either do:

if pnl[company].tail(1)['Active'].any()=='1':
  print 'yay'

要进行字符串比较，或修复数据，但它已被阅读或者生成。

To do a string comparison, or fix the data however it was read or generated.

或者执行：

pnl['Company']['Active'] = pnl['Company']['Active'].astype(int)

要转换列的 dtype ，以便您的比较更正确。

To convert the dtype of the column so that your comparison is more correct.

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