Pandas DataFrame apply() ValueError:要解包的值太多(预期为 2)
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【中文标题】Pandas DataFrame apply() ValueError:要解包的值太多(预期为 2)【英文标题】:Pandas DataFrame apply() ValueError: too many values to unpack (expected 2) 【发布时间】:2016-05-24 05:30:45 【问题描述】:我刚开始接触 Python,虽然我很兴奋,但似乎我离 Python 思维还很远。
这是一个方法的例子,它到处都是“次优”这个词。 虽然这对于我相对较小的数据集来说已经足够了,但我想知道如何才能更好地编写它?
import pandas as pd
from pandas import DataFrame
# create sample log data frame
lg = pd.DataFrame(['Access violation at address 00A97...',
'Try to edit the splines or change...',
'Access violation at address 00F2B...',
'Please make sure the main electro...'], columns=['lg_msg'])
# define message classification
err_messages = [['Access violation', 'ACC-VIOL', 'PROG'],
['Please make sure th', 'ELE-NOT-PLACED', 'MOD'],
['Try to edit the splines', 'TRY-EDIT-SPLINES', 'MOD']]
# lookup code
def message_code(msg_text):
for msg in err_messages:
if msg_text.startswith(msg[0]):
return msg[1]
return ''
# lookup type
def message_type(msg_text):
for msg in err_messages:
if msg_text.startswith(msg[0]):
return msg[2]
return ''
lg['msg_code'] = lg['lg_msg'].apply(lambda x: message_code(x))
lg['msg_type'] = lg['lg_msg'].apply(lambda x: message_type(x))
我尝试创建一个函数来计算日志条目代码并立即键入:
def message_code_type(msg_text):
for msg in err_messages:
if msg_text.startswith(msg[0]):
return (msg[1], msg[2])
return ('', '')
lg['msg_code'], lg['msg_type'] = lg['lg_msg'].apply(lambda x: message_code_type(x))
但得到:
---------------------------------------------------------------------------
ValueError Traceback (most recent call last)
<ipython-input-18-72f97d857539> in <module>()
----> 1 lg['msg_code'], lg['msg_code'] = lg['lg_msg'].apply(lambda x: message_code_type(x))
ValueError: too many values to unpack (expected 2)
有没有办法不遍历数据框两次?
我们将不胜感激。
import sys
print(sys.version)
3.5.1 |Anaconda 2.4.0 (64-bit)| (default, Jan 29 2016, 15:01:46) [MSC v.1900 64 bit (AMD64)]
pd.__version__
'0.17.1'
【问题讨论】:
【参考方案1】:使用 itertools 模块中的izip
试试这个:
from itertools import izip
lg['msg_code'], lg['msg_code'] = izip(*lg['lg_msg'].apply(lambda x: message_code_type(x)))
In [21]: lg
Out[21]:
lg_msg msg_code
0 Access violation at address 00A97... PROG
1 Try to edit the splines or change... MOD
2 Access violation at address 00F2B... PROG
3 Please make sure the main electro... MOD
抱歉,这是2.7,你应该可以使用内置的zip
lg['msg_code'], lg['msg_type'] = zip(*lg['lg_msg'].apply(lambda x: message_code_type(x)))
lg_msg msg_code msg_type
0 Access violation at address 00A97... ACC-VIOL PROG
1 Try to edit the splines or change... TRY-EDIT-SPLINES MOD
2 Access violation at address 00F2B... ACC-VIOL PROG
3 Please make sure the main electro... ELE-NOT-PLACED MOD
【讨论】:
谢谢,会试试的!一件事......我的错误,两个目标列具有相同的名称,这导致单个 msg_code 列。已经编辑了我的问题。 很遗憾,我的环境好像没有itertools[Anaconda3] C:\Users\[snip]>pip install itertools Collecting itertools Could not find a version that satisfies the requirement itertools (from versions: ) No matching distribution found for itertools
你不必导入 itertools 在 python3 中使用zip
,它是内置的。查看我发布的第二个链接中的示例。这个,特别是:x2, y2 = zip(*zip(x, y))
。这是使用zip
和map
的another SO question。以上是关于Pandas DataFrame apply() ValueError:要解包的值太多(预期为 2)的主要内容,如果未能解决你的问题,请参考以下文章
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