Python 按日期对 Pandas 数据框进行排序
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Sort Pandas Dataframe by Date
提问by nicholas.reichel
I have a pandas dataframe as follows:
我有一个熊猫数据框如下：
Symbol Date
A 02/20/2015
A 01/15/2016
A 08/21/2015
I want to sort it by Date, but the column is just an object.
我想按 排序Date，但该列只是一个object.
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.
我试图将该列设为日期对象，但遇到了该格式不是所需格式的问题。需要的格式是2015-02-20,等。
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.
所以现在我想弄清楚如何让 numpy 将“美国”日期转换为 ISO 标准，以便我可以将它们设为日期对象，以便我可以对它们进行排序。
How would I convert these american dates into ISO standard, or is there a more straight forward method I'm missing within pandas?
我如何将这些美国日期转换为 ISO 标准，或者是否有我在熊猫中缺少的更直接的方法？
采纳答案by JAB
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.
您可以使用pd.to_datetime()转换为日期时间对象。它需要一个格式参数，但在你的情况下，我认为你不需要它。
>>> 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
For future search, you can change the sort statement:
对于将来的搜索，您可以更改排序语句：
>>> 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
回答by LondonRob
@JAB's answeris fast and concise. But it changes the DataFrameyou are trying to sort, which you may or may not want.
@JAB 的回答快速而简洁。但它改变了DataFrame您尝试排序的内容，您可能想要也可能不想要。
(Note: You almost certainly willwant it, because your date columns should be dates, not strings!)
（注意：您几乎肯定会想要它，因为您的日期列应该是日期，而不是字符串！）
In the unlikely event that you don't want to change the dates into dates, you can also do it a different way.
万一您不想将日期更改为日期，您也可以采用不同的方式。
First, get the index from your sorted Datecolumn:
首先，从排序的Date列中获取索引：
In [25]: pd.to_datetime(df.Date).order().index
Out[25]: Int64Index([0, 2, 1], dtype='int64')
Then use it to index your original DataFrame, leaving it untouched:
然后用它来索引你的原件DataFrame，保持原样：
In [26]: df.ix[pd.to_datetime(df.Date).order().index]
Out[26]:
Date Symbol
0 2015-02-20 A
2 2015-08-21 A
1 2016-01-15 A
Magic!
魔法！
Note:for Pandas versions 0.20.0 and later, use locinstead of ix, which is now deprecated.
注意：对于 Pandas 0.20.0 及更高版本，使用loc代替ix，现在已弃用。
回答by Reveille
sortmethod has been deprecatedand replaced with sort_values. After converting to datetime object using df['Date']=pd.to_datetime(df['Date'])
sort方法已被弃用并替换为sort_values. 使用转换为日期时间对象后df['Date']=pd.to_datetime(df['Date'])
df.sort_values(by=['Date'])
Note: to sort in-placeand/or in a descending order (the most recent first):
注意：就地和/或降序排序（最近的第一个）：
df.sort_values(by=['Date'], inplace=True, ascending=False)
回答by Manthra
The data containing the date column can be read by using the below code:
可以使用以下代码读取包含日期列的数据：
data = pd.csv(file_path,parse_dates=[date_column])
Once the data is read by using the above line of code, the column containing the information about the date can be accessed using pd.date_time()like:
使用上述代码行读取数据后，可以使用以下方法访问包含有关日期信息的列pd.date_time()：
pd.date_time(data[date_column], format = '%d/%m/%y')
to change the format of date as per the requirement.
根据要求更改日期格式。
