pandas 计算相同最近值之间的时间跨度

Question

我是 python 用户。有一个 excel 这样的：

time    size   
2017-08-16 00:00:00 12    
2017-08-16 00:01:00 12    
2017-08-16 00:02:00 24   
2017-08-16 00:03:00 24    
2017-08-16 00:04:00 36   
2017-08-16 00:05:00 24    
2017-08-16 00:06:00 36    
2017-08-16 00:07:00 24    
2017-08-16 00:08:00 24    
2017-08-16 00:09:00 24

想计算出最近的相同数字之间的时间跨度，如下所示：

    time    size   timespan
    2017-08-16 00:00:00 12    0
    2017-08-16 00:01:00 12    60
    2017-08-16 00:02:00 24    0
    2017-08-16 00:03:00 24    60
    2017-08-16 00:04:00 36    0
    2017-08-16 00:05:00 24    0
    2017-08-16 00:06:00 36    0
    2017-08-16 00:07:00 24    0
    2017-08-16 00:08:00 24    0
    2017-08-16 00:09:00 24    120

请注意中间的数字 24 被忽略了。能用在pandas最好。

Answer 1

这里假设你先把excel文件导出到csv，比如time.csv

time,size
2017-08-16 00:00:00, 12    
2017-08-16 00:01:00, 12    
2017-08-16 00:02:00, 24   
2017-08-16 00:03:00, 24    
2017-08-16 00:04:00, 36   
2017-08-16 00:05:00, 24    
2017-08-16 00:06:00, 36    
2017-08-16 00:07:00, 24    
2017-08-16 00:08:00, 24    
2017-08-16 00:09:00, 24

解决方法如下。主要思想是当size与前一个相同但与下一个不同时，需要计算一个结果值。

import pandas as pd                                                                
from datetime import datetime                                                      

a = pd.read_csv('time.csv')                                                        
times = [datetime.strptime(x, '%Y-%m-%d %H:%M:%S') for x in a['time']]             

aa = list(a['size']) + [None]                                                      
res = [0] * len(a)                                                                 

prev = None                                                                        
for i, x in enumerate(a['size']):                                                  
    if x != prev:                                                                  
        begin_time = times[i]                                                      
    elif x != aa[i + 1]:                                                           
        res[i] = (times[i] - begin_time).seconds                                   
    prev = x                                                                       
print res

输出为[0, 60, 0, 60, 0, 0, 0, 0, 0, 120]

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