Python/Pandas仅将字符串转换为时间 [英] Python/Pandas convert string to time only

问题描述

我在Python 2.7中具有以下Pandas数据框.

I have the following Pandas dataframe in Python 2.7.

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

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

此数据框来自* .csv文件.我使用Pandas作为Pandas数据框读取* .csv文件.当我使用print dfc.dtypes时，它向我显示列Time_of_Sail的数据类型为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.

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_Sail has a datatype object. I would like to convert this column to datetime datatype BUT I only want the time part - I don't want the year, month, date.

我可以尝试:

dfc['Time_of_Sail'] = pd.to_datetime(dfc['Time_of_Sail'])
dfc['Time_of_Sail'] = [time.time() for time in dfc['Time_of_Sail']]

但是问题是，当我运行print dfc.dtypes时，它仍然显示列Time_of_Sail是object.

but the problem is that the when I run print dfc.dtypes it still shows that the column Time_of_Sail is object.

是否可以将此列转换为只有时间的日期时间格式?

Is there a way to convert this column into a datetime format that only has the time?

其他信息:

要创建上述数据框并输出，这也可以:

To create the above dataframe and output, this also works:

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

推荐答案

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']]

可以写为:

dfc['Time_of_Sail'] = pd.to_datetime(dfc['Time_of_Sail'],format= '%H:%M:%S' ).dt.time

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