英文:
Using the default and specifying the same default value explicitly give different results in pd.wide_to_long
问题
我正在将DataFrame从宽格式转换为长格式。但是，在两种情况下，我得到了不同的结果，这两种情况应该是相同的 - 请参见下面的代码：
import pandas as pd
import numpy as np
d_test = pd.DataFrame({"id": [1,2,3,5], "q1": [1,4,4,2], "q2": [4,np.nan,9,0]}, index=["a","b","c","d"])
# 返回一个空的DataFrame作为结果
pd.wide_to_long(d_test, stubnames=["q"], suffix=r"\d+", i="id", j="time")
# 这个可以正常工作：
pd.wide_to_long(d_test, stubnames=["q"], i="id", j="time")
请注意，这两行代码是相同的：在文档中，您可以看到suffix参数的默认值与我明确指定的值相同。
有人可以帮助我理解这里发生了什么问题吗？
英文:
I was reshaping a DataFrame from wide to long format. However I get different results in two cases which should be identical - see below
import pandas as pd
import numpy as np
d_test = pd.DataFrame({"id": [1,2,3,5], "q1": [1,4,4,2], "q2": [4,np.nan,9,0]}, index=["a","b","c","d"])
# Gives an empty DataFrame as result
pd.wide_to_long(d_test,stubnames=["q"], suffix=r"\\d+", i="id", j="time")
# This works:
pd.wide_to_long(d_test,stubnames=["q"], i="id", j="time")
Note that both lines are the same: In the documentation you can see that the default value for the suffix argument is identical to the one I specified explicitly.
Can someone help me in understanding what went wrong here?
答案1
得分: 2
你错误地转义了你的正则表达式：r"\\d+" 表示一个字面上的 \ 后跟一个或多个 d。
请注意，wide_to_long 文档使用的是 '\\d+'，而不是 r'\\d+'。
pd.wide_to_long(d_test, stubnames=['q'], suffix=r'\d+', i='id', j='time')
# 或者
pd.wide_to_long(d_test, stubnames=['q'], suffix='\\d+', i='id', j='time')
输出：
q
id time
1 1 1.0
2 1 4.0
3 1 4.0
5 1 2.0
1 2 4.0
2 2 NaN
3 2 9.0
5 2 0.0
英文:
You incorrectly escape your regex: r"\\d+" means a literal \ followed by one or many d.
Note that the wide_to_long documentation uses '\\d+', not r'\\d+'.
pd.wide_to_long(d_test, stubnames=['q'], suffix=r'\d+', i='id', j='time')
# or
pd.wide_to_long(d_test, stubnames=['q'], suffix='\\d+', i='id', j='time')
Output:
q
id time
1 1 1.0
2 1 4.0
3 1 4.0
5 1 2.0
1 2 4.0
2 2 NaN
3 2 9.0
5 2 0.0
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