按日期对 pandas 数据框进行排序

问题描述

我有一个熊猫数据框，如下所示:

I have a pandas dataframe as follows:

Symbol  Date
A       02/20/2015
A       01/15/2016
A       08/21/2015

我想按Date对其进行排序，但该列只是一个object.

I want to sort it by Date, but the column is just an object.

我试图将列设置为日期对象，但是遇到了一个问题，即该格式不是所需的格式.所需的格式为2015-02-20,等.

I tried to make the column a date object, but I ran into an issue where that format is not the format needed. The format needed is 2015-02-20, etc.

所以现在我想弄清楚如何让numpy将美国"日期转换为ISO标准，以便可以使它们成为日期对象，从而可以对它们进行排序.

So now I'm trying to figure out how to have numpy convert the 'American' dates into the ISO standard, so that I can make them date objects, so that I can sort by them.

我该如何将这些美国日期转换为ISO标准，或者熊猫中还缺少我更直接的方法?

How would I convert these american dates into ISO standard, or is there a more straight forward method I'm missing within pandas?

推荐答案

您可以使用pd.to_datetime()转换为日期时间对象.它带有一个format参数，但是在您的情况下，我认为您不需要它.

You can use pd.to_datetime() to convert to a datetime object. It takes a format parameter, but in your case I don't think you need it.

>>> import pandas as pd
>>> df = pd.DataFrame( {'Symbol':['A','A','A'] ,
    'Date':['02/20/2015','01/15/2016','08/21/2015']})
>>> df
         Date Symbol
0  02/20/2015      A
1  01/15/2016      A
2  08/21/2015      A
>>> df['Date'] =pd.to_datetime(df.Date)
>>> df.sort('Date') # This now sorts in date order
        Date Symbol
0 2015-02-20      A
2 2015-08-21      A
1 2016-01-15      A

对于以后的搜索，您可以更改sort语句:

For future search, you can change the sort statement:

>>> df.sort_values(by='Date') # This now sorts in date order
        Date Symbol
0 2015-02-20      A
2 2015-08-21      A
1 2016-01-15      A

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