7
pandas 怎么对比当前行的前面 7 天的所有某列的数字？
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商场每天销售额都有记录（按天统计），其中有一列是总销售额(total)，现需求是：用总销售额计算每一天与过去 N 天（例如一周 7 天）进行对比，找出两个结果：
1 当天是不是过去一周（ 7 ）销售额最低的
2 如果不是，过去一周哪天最低的销售额是多少？
我尝试过用遍历 range(1, 8)，然后 shift(1), shift(2) 这样总感觉不太科学，不知道有各位大佬有更加方便的办法？
1 当天是不是过去一周（ 7 ）销售额最低的
2 如果不是，过去一周哪天最低的销售额是多少？
我尝试过用遍历 range(1, 8)，然后 shift(1), shift(2) 这样总感觉不太科学，不知道有各位大佬有更加方便的办法？
2 条回复 • 2021-11-11 00:38:01 +08:00
keroppi 8 小时 38 分钟前
我目前自己写的代码（第 2 个要求还没搞）
```
for i in range(1, end_num):
df['prev_row'] = df['total'].shift(i)
df['range_compare_result'] = df['total'].lt(df['prev_row'])
del df['prev_row']
# end for
```
```
for i in range(1, end_num):
df['prev_row'] = df['total'].shift(i)
df['range_compare_result'] = df['total'].lt(df['prev_row'])
del df['prev_row']
# end for
```
necomancer 7 小时 34 分钟前
In [2]: ret = []
In [2]: for i in range(7, a.shape[0]+1):
...: m = np.argmin(a[i-7:i]) +i -7
...: ret.append((m, a[m], m==i-1))
...:
In [3]: ret
Out[3]:
[(4, 0.1070058697941636, False), # (绝对索引，值，当日是否为当周（前 7 日）最低）
(4, 0.1070058697941636, False),
(4, 0.1070058697941636, False),
(4, 0.1070058697941636, False),
(4, 0.1070058697941636, False),
(7, 0.38082268305528855, False),
(7, 0.38082268305528855, False),
(13, 0.3198102115371413, True),
(13, 0.3198102115371413, False),
(15, 0.26007158139013975, True),
(15, 0.26007158139013975, False),
(15, 0.26007158139013975, False),
(18, 0.1774755070886418, True),
(18, 0.1774755070886418, False)]
In [4]: a
Out[4]:
array([0.59171944, 0.95287085, 0.56036765, 0.91771266, 0.10700587,
0.67920182, 0.40034268, 0.38082268, 0.81140219, 0.78271362,
0.43178875, 0.7328393 , 0.93324926, 0.31981021, 0.74938937,
0.26007158, 0.33768583, 0.78881252, 0.17747551, 0.27862649])
In [2]: for i in range(7, a.shape[0]+1):
...: m = np.argmin(a[i-7:i]) +i -7
...: ret.append((m, a[m], m==i-1))
...:
In [3]: ret
Out[3]:
[(4, 0.1070058697941636, False), # (绝对索引，值，当日是否为当周（前 7 日）最低）
(4, 0.1070058697941636, False),
(4, 0.1070058697941636, False),
(4, 0.1070058697941636, False),
(4, 0.1070058697941636, False),
(7, 0.38082268305528855, False),
(7, 0.38082268305528855, False),
(13, 0.3198102115371413, True),
(13, 0.3198102115371413, False),
(15, 0.26007158139013975, True),
(15, 0.26007158139013975, False),
(15, 0.26007158139013975, False),
(18, 0.1774755070886418, True),
(18, 0.1774755070886418, False)]
In [4]: a
Out[4]:
array([0.59171944, 0.95287085, 0.56036765, 0.91771266, 0.10700587,
0.67920182, 0.40034268, 0.38082268, 0.81140219, 0.78271362,
0.43178875, 0.7328393 , 0.93324926, 0.31981021, 0.74938937,
0.26007158, 0.33768583, 0.78881252, 0.17747551, 0.27862649])
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