说我有一个如下所示的列表:
[(datetime.datetime(2013, 8, 8, 1, 20, 15), 2060), (datetime.datetime(2013, 8, 9, 1, 6, 14), 2055), (datetime.datetime(2013, 8, 9, 1, 21, 1), 2050), (datetime.datetime(2013, 8, 10, 1, 5, 49), 2050), (datetime.datetime(2013, 8, 10, 1, 19, 51), 2050), (datetime.datetime(2013, 8, 11, 2, 4, 53), 2050), (datetime.datetime(2013, 8, 12, 0, 29, 45), 2050), (datetime.datetime(2013, 8, 12, 0, 44, 13), 2050), (datetime.datetime(2013, 8, 13, 0, 34, 13), 2050), (datetime.datetime(2013, 8, 13, 0, 47, 29), 2050), (datetime.datetime(2013, 8, 14, 1, 30, 39), 2050), (datetime.datetime(2013, 8, 14, 1, 33, 51), 2050), (datetime.datetime(2013, 8, 15, 0, 41, 1), 2050), (datetime.datetime(2013, 8, 15, 0, 54, 45), 2050), (datetime.datetime(2013, 8, 16, 0, 29, 57), 1950), (datetime.datetime(2013, 8, 16, 0, 43, 11), 1950), (datetime.datetime(2013, 8, 17, 0, 27, 4), 1950), (datetime.datetime(2013, 8, 17, 0, 42, 30), 1950), (datetime.datetime(2013, 8, 18, 0, 26, 26), 1950), (datetime.datetime(2013, 8, 18, 0, 43, 11), 1950), (datetime.datetime(2013, 8, 19, 0, 41, 49), 1950), (datetime.datetime(2013, 8, 20, 1, 10, 23), 1950), (datetime.datetime(2013, 8, 20, 1, 23, 44), 1950), (datetime.datetime(2013, 8, 21, 0, 47, 25), 1950), (datetime.datetime(2013, 8, 21, 1, 0, 12), 1950), (datetime.datetime(2013, 8, 22, 0, 45, 21), 1950), (datetime.datetime(2013, 8, 22, 1, 4, 33), 1950), (datetime.datetime(2013, 8, 23, 0, 51, 27), 1950), (datetime.datetime(2013, 8, 23, 1, 6, 36), 1950), (datetime.datetime(2013, 8, 24, 0, 41, 3), 1950), (datetime.datetime(2013, 8, 24, 0, 53, 14), 1950), (datetime.datetime(2013, 8, 25, 0, 29, 24), 1950), (datetime.datetime(2013, 8, 25, 0, 42, 40), 1950), (datetime.datetime(2013, 8, 26, 0, 28, 13), 1950), (datetime.datetime(2013, 8, 26, 0, 43, 30), 1950), (datetime.datetime(2013, 8, 27, 0, 30, 1), 1950), (datetime.datetime(2013, 8, 27, 0, 43, 43), 1950), (datetime.datetime(2013, 8, 28, 0, 33, 19), 1950), (datetime.datetime(2013, 8, 28, 0, 49, 11), 1950), (datetime.datetime(2013, 8, 29, 0, 26, 49), 1950), (datetime.datetime(2013, 8, 29, 0, 41, 21), 1950), (datetime.datetime(2013, 8, 30, 0, 26, 13), 1950), (datetime.datetime(2013, 8, 30, 0, 42, 9), 1950), (datetime.datetime(2013, 8, 31, 0, 23, 40), 1950), (datetime.datetime(2013, 8, 31, 0, 39, 49), 1950), (datetime.datetime(2013, 9, 1, 0, 22, 2), 1950), (datetime.datetime(2013, 9, 1, 0, 38, 16), 1950), (datetime.datetime(2013, 9, 2, 0, 21, 2), 1950), (datetime.datetime(2013, 9, 2, 0, 36, 19), 1950), (datetime.datetime(2013, 9, 3, 0, 22, 16), 1950), (datetime.datetime(2013, 9, 3, 0, 39, 2), 1900)]
很明显,你可以看到这是一个元组列表,每个元组中的第一个元素是一个时间戳。已经格式良好,由:生成
datetime.strptime(record[0], timeFormat)
第二个元素是监控值。但是,每天可能会有多个记录。例如,datetime.datetime(2013,8,9 ..)上有两条记录,它们有两个不同的值2055和2050.我想要的是实际上每天的最大值。 所以在这种情况下。 2055年将是(2013年,8,9)的唯一记录。
我想知道在Python中有没有方便的方法来做到这一点。有点像mysql的东西:
select
date(timestamp),
max(value)
from table
group by date(timestamp)
mysql语句只是为了展示这个想法,我绝对想要一个python解决方案。
答案 0 :(得分:8)
>>> records = [(datetime.datetime(2013, 8, 8, 1, 20, 15), 2060), ....]
>>> import itertools
>>> [(dt, max(v for d, v in grp)) for dt, grp in itertools.groupby(records, key=lambda x: x[0].date())]
[(datetime.date(2013, 8, 8), 2060),
(datetime.date(2013, 8, 9), 2055),
(datetime.date(2013, 8, 10), 2050),
...
]
注意:假设记录已排序。如果没有,您应该先按日期对它们进行排序。
答案 1 :(得分:2)
您可以使用collections.defaultdict
(这将适用于O(N)
时间内的已排序和未排序数据:
>>> from collections import defaultdict
>>> lis = [(datetime.datetime(2013, 8, 8, 1, 20, 15), 2060), (datetime.datetime(2013, 8, 9, 1, 6, 14), 2055), (datetime.datetime(2013, 8, 9, 1, 21, 1), 2050), (datetime.datetime(2013, 8, 10, 1, 5, 49), 2050), (datetime.datetime(2013, 8, 10, 1, 19, 51), 2050), (datetime.datetime(2013, 8, 11, 2, 4, 53), 2050), (datetime.datetime(2013, 8, 12, 0, 29, 45), 2050), (datetime.datetime(2013, 8, 12, 0, 44, 13), 2050), (datetime.datetime(2013, 8, 13, 0, 34, 13), 2050), (datetime.datetime(2013, 8, 13, 0, 47, 29), 2050), (datetime.datetime(2013, 8, 14, 1, 30, 39), 2050), (datetime.datetime(2013, 8, 14, 1, 33, 51), 2050), (datetime.datetime(2013, 8, 15, 0, 41, 1), 2050), (datetime.datetime(2013, 8, 15, 0, 54, 45), 2050), (datetime.datetime(2013, 8, 16, 0, 29, 57), 1950), (datetime.datetime(2013, 8, 16, 0, 43, 11), 1950), (datetime.datetime(2013, 8, 17, 0, 27, 4), 1950), (datetime.datetime(2013, 8, 17, 0, 42, 30), 1950), (datetime.datetime(2013, 8, 18, 0, 26, 26), 1950), (datetime.datetime(2013, 8, 18, 0, 43, 11), 1950), (datetime.datetime(2013, 8, 19, 0, 41, 49), 1950), (datetime.datetime(2013, 8, 20, 1, 10, 23), 1950), (datetime.datetime(2013, 8, 20, 1, 23, 44), 1950), (datetime.datetime(2013, 8, 21, 0, 47, 25), 1950), (datetime.datetime(2013, 8, 21, 1, 0, 12), 1950), (datetime.datetime(2013, 8, 22, 0, 45, 21), 1950), (datetime.datetime(2013, 8, 22, 1, 4, 33), 1950), (datetime.datetime(2013, 8, 23, 0, 51, 27), 1950), (datetime.datetime(2013, 8, 23, 1, 6, 36), 1950), (datetime.datetime(2013, 8, 24, 0, 41, 3), 1950), (datetime.datetime(2013, 8, 24, 0, 53, 14), 1950), (datetime.datetime(2013, 8, 25, 0, 29, 24), 1950), (datetime.datetime(2013, 8, 25, 0, 42, 40), 1950), (datetime.datetime(2013, 8, 26, 0, 28, 13), 1950), (datetime.datetime(2013, 8, 26, 0, 43, 30), 1950), (datetime.datetime(2013, 8, 27, 0, 30, 1), 1950), (datetime.datetime(2013, 8, 27, 0, 43, 43), 1950), (datetime.datetime(2013, 8, 28, 0, 33, 19), 1950), (datetime.datetime(2013, 8, 28, 0, 49, 11), 1950), (datetime.datetime(2013, 8, 29, 0, 26, 49), 1950), (datetime.datetime(2013, 8, 29, 0, 41, 21), 1950), (datetime.datetime(2013, 8, 30, 0, 26, 13), 1950), (datetime.datetime(2013, 8, 30, 0, 42, 9), 1950), (datetime.datetime(2013, 8, 31, 0, 23, 40), 1950), (datetime.datetime(2013, 8, 31, 0, 39, 49), 1950), (datetime.datetime(2013, 9, 1, 0, 22, 2), 1950), (datetime.datetime(2013, 9, 1, 0, 38, 16), 1950), (datetime.datetime(2013, 9, 2, 0, 21, 2), 1950), (datetime.datetime(2013, 9, 2, 0, 36, 19), 1950), (datetime.datetime(2013, 9, 3, 0, 22, 16), 1950), (datetime.datetime(2013, 9, 3, 0, 39, 2), 1900)]
>>> dic = defaultdict(list)
for dt, val in lis:
dic[dt.date()].append(val)
...
>>> for k, v in dic.iteritems():
print k, max(v)
...
2013-08-20 1950
2013-08-15 2050
2013-08-22 1950
2013-08-09 2055
2013-08-16 1950
2013-08-11 2050
2013-08-18 1950
2013-09-03 1950
2013-09-01 1950
...
正如@hughdbrown提到的更好的方法是:
>>> dic = {}
>>> for dt, val in lis:
... dt = dt.date()
... dic[dt] = max(dic.get(dt,0), val)
...
>>> for k, v in dic.iteritems():
... print k,v
...
2013-08-20 1950
2013-08-15 2050
2013-08-22 1950
2013-08-09 2055
2013-08-16 1950
2013-08-11 2050
2013-08-18 1950
2013-09-03 1950
2013-09-01 1950
...