如何按价值对字典进行排序？

2018-05-30 00:04:23

我有一个从数据库中的两个字段中读取值的字典：一个字符串字段和一个数字字段。字符串字段是唯一的，所以这是字典的关键。

我可以对键进行排序，但是如何根据这些值进行排序？

注意：我已阅读Stack Overflow问题如何按Python中字典的值对字典列表进行排序？并可能可以改变我的代码有一个字典的列表，但因为我真的不需要一个字典的列表，我想知道是否有一个更简单的解决方案。

为了完整起见，我使用heapq发布了一个解决方案。请注意，此方法适用于数字和非数字值

>>> x = {1: 2, 3: 4, 4:3, 2:1, 0:0}
>>> x_items = x.items()
>>> heapq.heapify(x_items)
>>> #To sort in reverse order
>>> heapq.nlargest(len(x_items),x_items, operator.itemgetter(1))
[(3, 4), (4, 3), (1, 2), (2, 1), (0, 0)]
>>> #To sort in ascending order
>>> heapq.nsmallest(len(x_items),x_items, operator.itemgetter(1))
[(0, 0), (2, 1), (1, 2), (4, 3), (3, 4)]

months = {"January": 31, "February": 28, "March": 31, "April": 30, "May": 31,
          "June": 30, "July": 31, "August": 31, "September": 30, "October": 31,
          "November": 30, "December": 31}

def mykey(t):
    """ Customize your sorting logic using this function.  The parameter to
    this function is a tuple.  Comment/uncomment the return statements to test
    different logics.
    """
    return t[1]              # sort by number of days in the month
    #return t[1], t[0]       # sort by number of days, then by month name
    #return len(t[0])        # sort by length of month name
    #return t[0][-1]         # sort by last character of month name


# Since a dictionary can't be sorted by value, what you can do is to convert
# it into a list of tuples with tuple length 2.
# You can then do custom sorts by passing your own function to sorted().
months_as_list = sorted(months.items(), key=mykey, reverse=False)

for month in months_as_list:
    print month

正如Dilettant指出的那样，Python 3.6现在可以保持顺序！我想我会分享一个我写的函数，它简化了迭代（元组，列表，字典）的排序。在后一种情况下，您可以对键或值进行排序，并且可以将数字比较考虑在内。 只有> = 3.6！

当你尝试使用一个持有例如字符串和int的iterable时，sorted（）将会失败。当然你可以用str（）强制字符串比较。但是，在某些情况下，您希望进行实际的数字比较，其中12小于20 （字符串比较中不是这种情况）。所以我想出了以下几点。当你想要明确的数字比较时，你可以使用标志num_as_num ，它试图通过尝试将所有值转换为浮点数来进行明确的数字排序。如果成功，它会进行数字排序，否则它会求助于字符串比较。

对改进或推送请求的意见表示欢迎。

def sort_iterable(iterable, sort_on=None, reverse=False, num_as_num=False):
    def _sort(i):
      # sort by 0 = keys, 1 values, None for lists and tuples
      try:
        if num_as_num:
          if i is None:
            _sorted = sorted(iterable, key=lambda v: float(v), reverse=reverse)
          else:
            _sorted = dict(sorted(iterable.items(), key=lambda v: float(v[i]), reverse=reverse))
        else:
          raise TypeError
      except (TypeError, ValueError):
        if i is None:
          _sorted = sorted(iterable, key=lambda v: str(v), reverse=reverse)
        else:
          _sorted = dict(sorted(iterable.items(), key=lambda v: str(v[i]), reverse=reverse))

      return _sorted

    if isinstance(iterable, list):
      sorted_list = _sort(None)
      return sorted_list
    elif isinstance(iterable, tuple):
      sorted_list = tuple(_sort(None))
      return sorted_list
    elif isinstance(iterable, dict):
      if sort_on == 'keys':
        sorted_dict = _sort(0)
        return sorted_dict
      elif sort_on == 'values':
        sorted_dict = _sort(1)
        return sorted_dict
      elif sort_on is not None:
        raise ValueError(f"Unexpected value {sort_on} for sort_on. When sorting a dict, use key or values")
    else:
      raise TypeError(f"Unexpected type {type(iterable)} for iterable. Expected a list, tuple, or dict")

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