Python/Pandas 仅将字符串转换为时间
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Python/Pandas convert string to time only
提问by edesz
I have the following Pandas dataframe in Python 2.7.
我在 Python 2.7 中有以下 Pandas 数据框。
import pandas as pd
trial_num = [1,2,3,4,5]
sail_rem_time = ['11:33:11','16:29:05','09:37:56','21:43:31','17:42:06']
dfc = pd.DataFrame(zip(*[trial_num,sail_rem_time]),columns=['Temp_Reading','Time_of_Sail'])
print dfc
The dataframe looks like this:
数据框如下所示：
Temp_Reading Time_of_Sail
1 11:33:11
2 16:29:05
3 09:37:56
4 21:43:31
5 17:42:06
This dataframe comes from a *.csv file. I use Pandas to read in the *.csv file as a Pandas dataframe. When I use print dfc.dtypes, it shows me that the column Time_of_Sailhas a datatype object. I would like to convert this column to datetimedatatype BUT I only want the time part - I don't want the year, month, date.
此数据框来自 *.csv 文件。我使用 Pandas 将 *.csv 文件作为 Pandas 数据框读入。当我使用时print dfc.dtypes，它显示该列Time_of_Sail有一个数据类型object。我想将此列转换为datetime数据类型，但我只想要时间部分 - 我不想要年、月、日。
I can try this:
我可以试试这个：
dfc['Time_of_Sail'] = pd.to_datetime(dfc['Time_of_Sail'])
dfc['Time_of_Sail'] = [time.time() for time in dfc['Time_of_Sail']]
but the problem is that the when I run print dfc.dtypesit still shows that the column Time_of_Sailis object.
但问题是当我运行print dfc.dtypes它时仍然显示该列Time_of_Sail是object.
Is there a way to convert this column into a datetime format that only has the time?
有没有办法将此列转换为只有时间的日期时间格式？
Additional Information:
附加信息：
To create the above dataframe and output, this also works:
要创建上述数据框和输出，这也适用：
import pandas as pd
trial_num = [1,2,3,4,5]
sail_rem_time = ['11:33:11','16:29:05','09:37:56','21:43:31','17:42:06']
data = [
[trial_num[0],sail_rem_time[0]],
[trial_num[1],sail_rem_time[1]],[trial_num[2],sail_rem_time[2]],
[trial_num[3],sail_rem_time[3]]
]
dfc = pd.DataFrame(data,columns=['Temp_Reading','Time_of_Sail'])
dfc['Time_of_Sail'] = pd.to_datetime(dfc['Time_of_Sail'])
dfc['Time_of_Sail'] = [time.time() for time in dfc['Time_of_Sail']]
print dfc
print dfc.dtypes
回答by Merlin
These two lines:
这两行：
dfc['Time_of_Sail'] = pd.to_datetime(dfc['Time_of_Sail'])
dfc['Time_of_Sail'] = [time.time() for time in dfc['Time_of_Sail']]
Can be written as:
可以写成：
dfc['Time_of_Sail'] = pd.to_datetime(dfc['Time_of_Sail'],format= '%H:%M:%S' ).dt.time
回答by Bhavani Prasad Basuthkar
Using to_timedelta,we can convert string to time format(timedelta64[ns]) by specifying units as second,min etc.,
使用 to_timedelta，我们可以通过将单位指定为秒、分钟等，将字符串转换为时间格式（timedelta64[ns]），
dfc['Time_of_Sail'] = pd.to_timedelta(dfc['Time_of_Sail'], unit='s')
回答by Moe Chughtai
If you just want a simple conversion you can do the below:
如果您只是想要一个简单的转换，您可以执行以下操作：
import datetime as dt
dfc.Time_of_Sail = dfc.Time_of_Sail.astype(dt.datetime)
or you could add a holder string to your time column as below, and then convert afterwards using an apply function:
或者您可以将一个持有者字符串添加到您的时间列，如下所示，然后使用应用函数进行转换：
dfc.Time_of_Sail = dfc.Time_of_Sail.apply(lambda x: '2016-01-01 ' + str(x))
dfc.Time_of_Sail = pd.to_datetime(dfc.Time_of_Sail).apply(lambda x: dt.datetime.time(x))
回答by ferengi
This seems to work:
这似乎有效：
dfc['Time_of_Sail'] = pd.to_datetime(dfc['Time_of_Sail'], format='%H:%M:%S' ).apply(pd.Timestamp)
dfc['Time_of_Sail'] = pd.to_datetime(dfc['Time_of_Sail'], format='%H:%M:%S' ).apply(pd.Timestamp)
