Python 查询最旧日期列表

Question

我的查询在列表中返回以下内容:

"Alex";"275467125";"2015-02-03 02:55:36-05";"1"
"Alex";"275467125";"2015-01-13 02:09:39-05";"1"
"Alex";"275467125";"2015-01-05 04:13:35-05";"1"
"Alex";"275467125";"2014-12-27 04:55:47-05";"1"
"Alex";"275467125";"2014-12-27 04:54:52-05";"1"
"Alex";"275467125";"2014-12-07 03:13:24-05";"1"
"Alex";"275467125";"2014-12-04 03:34:56-05";"1"
"Alex";"275467125";"2014-12-02 04:16:33-05";"1"
"Ali";"275464747";"2016-02-17 10:52:12-05";"2"
"Alladin";"275467455";"2016-03-13 06:51:52-04";"2"
"Alladin";"275467455";"2016-03-13 06:51:47-04";"2"
"Anna";"275467401";"2016-03-26 03:56:41-04";"1"
"Anna";"275467401";"2016-03-26 03:55:21-04";"1"
"Anna";"275467401";"2016-03-21 23:04:28-04";"1"
"Anna";"275467401";"2016-02-12 13:24:44-05";"1"
"Anna";"275467401";"2015-12-03 08:20:35-05";"1"
"Anna";"275467401";"2015-11-09 04:18:27-05";"1"
"Anna";"275467401";"2015-11-09 04:11:59-05";"1"
"Anna";"275467401";"2015-09-13 21:27:12-04";"1"

我想创建一个人名字典，其中包含他们拥有的最旧记录。我发现:

oldestlist = {d[0]:d[2] for d in records}

这会返回正确的答案，但我担心的是，如果我看到的列表未按日期/时间降序排列，它将无法提供正确的答案。创建包含名称和最早日期的字典的最佳方法是什么？

Answer 1

您不需要对任何数据进行排序，只需使用defaultdict并检查当前日期与任何新日期并相应更新:

s = """"Alex";"275467125";"2015-02-03 02:55:36-05";"1"
"Alex";"275467125";"2015-01-13 02:09:39-05";"1"
"Alex";"275467125";"2015-01-05 04:13:35-05";"1"
"Alex";"275467125";"2014-12-27 04:55:47-05";"1"
"Alex";"275467125";"2014-12-27 04:54:52-05";"1"
"Alex";"275467125";"2014-12-07 03:13:24-05";"1"
"Alex";"275467125";"2014-12-04 03:34:56-05";"1"
"Alex";"275467125";"2014-12-02 04:16:33-05";"1"
"Ali";"275464747";"2016-02-17 10:52:12-05";"2"
"Alladin";"275467455";"2016-03-13 06:51:52-04";"2"
"Alladin";"275467455";"2016-03-13 06:51:47-04";"2"
"Anna";"275467401";"2016-03-26 03:56:41-04";"1"
"Anna";"275467401";"2016-03-26 03:55:21-04";"1"
"Anna";"275467401";"2016-03-21 23:04:28-04";"1"
"Anna";"275467401";"2016-02-12 13:24:44-05";"1"
"Anna";"275467401";"2015-12-03 08:20:35-05";"1"
"Anna";"275467401";"2015-11-09 04:18:27-05";"1"
"Anna";"275467401";"2015-11-09 04:11:59-05";"1"
"Anna";"275467401";"2015-09-13 21:27:12-04";"1"
"""

import  csv
from collections import defaultdict

d = defaultdict(str)
for name,_, date, _ in csv.reader(s.splitlines(), delimiter=";"):
    if not d[name] or d[name] > date:
        d[name] = date


from pprint import pprint as pp

pp(dict(d))

输出:

 {'Alex': '2014-12-02 04:16:33-05',
 'Ali': '2016-02-17 10:52:12-05',
'Alladin': '2016-03-13 06:51:47-04',
'Anna': '2015-09-13 21:27:12-04'}

因为日期采用y-m-d 时间格式，所以可以安全地进行字典顺序比较。