Python groupby 无法按预期工作[重复]

我正在尝试读取一个 Excel 电子表格，其中包含以下格式的一些列：

column1__
column1__AccountName
column1__SomeOtherFeature
column2__blabla
column2_SecondFeat

我已经将一行的值保存为元组列表，其中元组是变量中的 (column_name, column_value)x.

现在我想将其分组如下：

result = { 
    'column__1': [list of (k,v) tuples, which keys start with 'column__1'],
    'column__2': [list of (k,v) tuples, which keys start with 'column__2']
}

但它没有给出预期的结果：

>>> from itertools import groupby

>>> x
[(u'My field one__AccountName', u'Lorem ipsum bla bla bla'),
 (u'My field one__AccountNumber', u'1111111222255555'),
 (u'My field two__Num', u'Num: 612312345'),
 (u'My field two', u'asdasdafassda'),
 (u'My field three__Beneficiary International Bank Account Number IBAN',
  u'IE111111111111111111111'),
 (u'My field one__BIC', u'BLEAHBLA1'),
 (u'My field three__company name', u'Company XYZ'),
 (u'My field two__BIC', u'ASDF333')]

>>> groups = groupby(x ,lambda (field, val): field.split('__')[0])

>>> grouped_fields = {key: list(val) for key, val in groups}

>>> grouped_fields

{u'My field one': [(u'My field one__BIC', u'BLEAHBLA1')],
 u'My field three': [(u'My field three__company name', u'Company XYZ')],
 u'My field two': [(u'My field two__BIC', u'ASDF333')]}

 >>> x[0]
(u'My field one__AccountName', u'Lorem ipsum bla bla bla')

>>> x[1]
(u'My field one__AccountNumber', u'1111111222255555')

>>> x[0][0].split('__')[0] == x[1][0].split('__')[0]
True

然而，它似乎适用于初始列表的另一个实例：

>>> y = [(u'x a b__2', 3), (u'x a b__', 1), (u'x a b__1', 2), (u'y a__1', 1), (u'y a__2', 2)]

>>> y
[(u'x__2', 3), (u'x__', 1), (u'x__1', 2), (u'y__1', 1), (u'y__2', 2)]

>>> groupes_y = groupby(y, lambda (k,v): k.split('__')[0])

>>> grouped_y = {key:list(val) for key, val in groupes_y}

>>> grouped_y

{u'x': [(u'x__2', 3), (u'x__', 1), (u'x__1', 2)],
 u'y': [(u'y__1', 1), (u'y__2', 2)]}

不知道我做错了什么。

As 文档说 https://docs.python.org/library/itertools.html#itertools.groupby，你应该申请groupby到已经使用相同排序的列表key as groupby itself:

key = lambda fv: fv[0].split('__')[0]
groups = groupby(sorted(x, key=key), key=key)

Then grouped_fields is:

{u'My field one': [(u'My field one__AccountName', u'Lorem ipsum bla bla bla'),
  (u'My field one__AccountNumber', u'1111111222255555'),
  (u'My field one__BIC', u'BLEAHBLA1')],
 u'My field three': [(u'My field three__Beneficiary International Bank Account Number IBAN',
   u'IE111111111111111111111'),
  (u'My field three__company name', u'Company XYZ')],
 u'My field two': [(u'My field two__Num', u'Num: 612312345'),
  (u'My field two', u'asdasdafassda'),
  (u'My field two__BIC', u'ASDF333')]}

在你的第二个例子中，碰巧的是y已经排序：

>>> y == sorted(y, key=key)
True