我每天都需要知道前一天的最大值是多少，例如：
帶日期的陣列
date = np.array(['05/12/2017', '05/12/2017', '05/13/2017', '05/13/2017', '05/13/2017',
'05/13/2017', '05/14/2017', '05/15/2017', '05/15/2017', '05/15/2017',
'05/15/2017', '05/15/2017', '05/16/2017', '05/16/2017', '05/16/2017',
'05/16/2017', '05/16/2017' '05/16/2017', '05/17/2017', '05/17/2017'])
具有值的陣列：
value = np.array([13, 4, 5, 4, 17, 8, 5, 9, 17, 6, 11, 16, 12, 7, 7, 12, 17, 10, 16, 14])
結果我需要：
result = np.array([0, 0, 13, 13, 13, 13, 17, 5, 5, 5, 5, 5, 17, 17, 17, 17, 17, 17, 17, 17])
uj5u.com熱心網友回復：
請注意，日期陣列中缺少逗號。
import numpy as np
from datetime import datetime, timedelta
from collections import defaultdict
dates = np.array(['05/12/2017', '05/12/2017', '05/13/2017', '05/13/2017', '05/13/2017',
'05/13/2017', '05/14/2017', '05/15/2017', '05/15/2017', '05/15/2017',
'05/15/2017', '05/15/2017', '05/16/2017', '05/16/2017', '05/16/2017',
'05/16/2017', '05/16/2017', '05/16/2017', '05/17/2017', '05/17/2017'])
values = np.array([13, 4, 5, 4, 17, 8, 5, 9, 17, 6, 11, 16, 12, 7, 7, 12, 17, 10, 16, 14])
parsed_dates = np.array([datetime.strptime(_, "%m/%d/%Y") for _ in dates])
dv = zip(parsed_dates, values)
max_dates = defaultdict(lambda: 0)
for date, value in dv:
max_dates[date] = max(value, max_dates[date])
one_day = timedelta(days=1)
result = np.array([max_dates[d - one_day] for d in parsed_dates])
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