Question

>>> a
[[1990, 51.3096170908506], [1992, 51.2635305924819], [1992, 51.3374119057099], [1992, 51.8759788779255], [1993, 51.1736475226503], [1993, 51.2227948371244], [1993, 51.2227948371244], [1993, 51.8494182515316], [1993, 51.8494182515316], [1994, 51.1741251939274], [1994, 51.88740455961], [1995, 51.1782277553216], [1996, 50.8955164985205], [1996, 50.8955164985205], [1996, 51.1376528237266], [1996, 51.1740979454], [1997, 50.8955819858876], [1997, 50.8983272540453], [1997, 51.8619829641787], [1997, 51.8619829641787]]

如何找到每年的最大纬度（python）：例如：

[1992, 51.8759788779255]

Answer 1

您可以使用collections.defaultdict(list)创建一个包含按年份分组的纬度的字典：

>>> import collections
>>> result = collections.defaultdict(list)
>>> for item in data:
...     result[item[0]].append(item[1])
...
>>> result
defaultdict(<type 'list'>, {1990: [51.3096170908506], 1992: [51.2635305924819, 51.3374119057099, 51.8759788779255], 1993: [51.1736475226503, 51.2227948371244, 51.2227948371244, 51.8494182515316, 51.8494182515316], 1994: [51.1741251939274, 51.88740455961], 1995: [51.1782277553216], 1996: [50.8955164985205, 50.8955164985205, 51.1376528237266, 51.1740979454], 1997: [50.8955819858876, 50.8983272540453, 51.8619829641787, 51.8619829641787]})
>>> for key, value in result.items():
...     print key, max(value)
...
1990 51.3096170909
1992 51.8759788779
1993 51.8494182515
1994 51.8874045596
1995 51.1782277553
1996 51.1740979454
1997 51.8619829642

此词典将年份作为键，将列表中的纬度作为值。然后，您可以迭代该字典的内容并使用max()获得该年度所有纬度范围内的最大纬度。

Answer 2

如果由于任何原因您不想使用collections.defaultdict，则必须使用dict.setdefault提供初始值：

a = [[1990, 51.3096170908506], [1992, 51.2635305924819],
     [1992, 51.3374119057099], [1992, 51.8759788779255],
     [1993, 51.1736475226503], [1993, 51.2227948371244],
     [1993, 51.2227948371244], [1993, 51.8494182515316],
     [1993, 51.8494182515316], [1994, 51.1741251939274],
     [1994, 51.88740455961], [1995, 51.1782277553216],
     [1996, 50.8955164985205], [1996, 50.8955164985205],
     [1996, 51.1376528237266], [1996, 51.1740979454],
     [1997, 50.8955819858876], [1997, 50.8983272540453],
     [1997, 51.8619829641787], [1997, 51.8619829641787]]

result = {}

for year, lat in a:
    result.setdefault(year, []).append(lat)

for year in result:
    print(year, max(result[year]))

'''
1990 51.3096170908506
1992 51.8759788779255
1993 51.8494182515316
1994 51.88740455961
1995 51.1782277553216
1996 51.1740979454
1997 51.8619829641787
'''

Answer 3

我可以尝试这种方式：

 >>> [sorted(x, key = lambda x: x[1], reverse=True)[0] for x in [[(y[0],y[1]) for y in a if y[0]==x] for x in values]]
    [(1990, 51.3096170908506), 
    (1992, 51.8759788779255), 
    (1993, 51.8494182515316), 
    (1994, 51.88740455961), 
    (1995, 51.1782277553216), 
    (1996, 51.1740979454), 
    (1997, 51.8619829641787)]
>>>

在具有相同第一个元素的嵌套列表中查找最大值

3 个答案: