根据时间戳对列表中的Json数据进行排序 [英] Sort Json data in list according to timestamp

问题描述

我正在加载数据(20个元素)到另一个加载的文件...在这里，我想根据我在list元素中使用的时间戳对这20个元素进行排序.

I am loading data(20 elements) to another file on load...here I want to sort these 20 elements according to timestamp I am using in list element.

import json
from collections import OrderedDict
import datetime
import os

if os.path.exists("qwerty.json"):
    record = json.load(open("qwerty.json", "r"), object_pairs_hook=OrderedDict)
else:
    record = OrderedDict({})

fo = open("foo.txt", "wb")
abc = list(record.items())[:20] 
print(abc)

command = ""
while command != 'exit':
    command = input('Enter a command(options: create,read,save): ')
    if command == "create":
        name = input('Enter name of the Student:')
        p = input('Student ID: ')
        a = input('Class: ')
        n = input('Marks: ')
        time = datetime.datetime.now().isoformat()

        record[name] = {'Student ID:': p, 'Class:': a, 'Marks': n, 'time': time }

    elif command == 'read':
        z = json.load(open("qwerty.json", "r"), object_pairs_hook=OrderedDict)
        print(z)

    elif command == 'save':
        json.dump(record, open('qwerty.json', "w"))

fo.close()

推荐答案

琐事:

由于您使用的是OrderedDict-您的记录已经按时间戳进行了排序(说实话-它们不是，但是保留了记录顺序).

Trivia:

Since you're using an OrderedDict - your records are already sorted by timestamp (to be honest - they're not, but recordses order is preserved).

代码中唯一的意外行为-当您创建"(覆盖)时，一行中有一名学生:

The only unexpected behaviour with your code - when you "create" (overwrite) existed one student in line:

record[name] = {'Student ID:': p, 'Class:': a, 'Marks': n, 'time': time }

并且if name in record:已经-顺序被破坏了，所以您关于排序的想法并不是毫无意义，但是我认为，仅要确定记录的顺序比每次对记录进行排序会更好，更合理.

And if name in record: already - order is broken, so your idea about sorting isn't a meaningless, but I think, that it's better and more rational to just be sure of the recordses order, than sort records each time.

方括号表示该对象是可下标的(例如，元组，列表，字典，字符串等). Subscriptable 表示此对象至少实现__getitem__()方法(在您的情况下为__setitem__()).

Square brackets after variable name means that this object is subscriptable (for e.g. tuple, list, dict, string and many more). Subscriptable means that this object at least implements the __getitem__() method (and __setitem__() in your case).

当您尝试从 subscriptable 对象(通过索引/键/任何东西)中提取内容时，第一种方法处理情况；而当您尝试覆盖某些内容时，第二种方法处理情况.

First method handles case, when you're trying to pull something from subscriptable object (by index/key/anything) and the second one - when you're trying to overwrite something.

我建议使用自定义类实现这种功能:

And I suggest to implement such a feature with custom class:

class OrderedTimeDict(OrderedDict):
    def __setitem__(self, key, value):
        if key in self:
            # if key is already exist - move it to the end
            self.move_to_end(key)
        # standard behaviour
        OrderedDict.__setitem__(self, key, value)

在您的代码中，仅使用此有序字典而不是基本有序！

and in your code just use this ordered dictionary instead of base ordered!

优点:无需排序，因为我们保持了所需的顺序.

Pros: No need to sort things, because we keep desired order.

缺点:如果您已经具有无序"数据-您需要对它进行一次排序.

Cons: If you're already has "unordered" data - you need to sort it once.

要按时间戳对有序的字典进行排序，可以使用以下功能:

To sort ordered dict by time stamp you can use this function:

def sort_by_timestamp(dict):
    return OrderedDict(sorted(dict.items(), key=lambda get_time_stamp: get_time_stamp[1]['time']))

参考文献:

• 在Python中，一个对象是否可以下标是什么意思?
• OrderedDict示例和食谱

References:

• In Python, what does it mean if an object is subscriptable or not?
• OrderedDict Examples and Recipes

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