满足条件时，制动for-loop

Question

我有熊猫df。Dataframe包含各种产品的信息，以及该产品在特定月份是否有销售

product  2021-01-01 00:00:00  2021-02-01 00:00:00  2021-03-01 00:00:00  2021-04-01 00:00:00  2021-05-01 00:00:00  2021-06-01 00:00:00  2021-07-01 00:00:00  2021-08-01 00:00:00  2021-09-01 00:00:00  2021-10-01 00:00:00  2021-11-01 00:00:00  2021-12-01 00:00:00  2022-01-01 00:00:00  2022-02-01 00:00:00  2022-03-01 00:00:00  2022-04-01 00:00:00  2022-05-01 00:00:00  2022-06-01 00:00:00  2022-07-01 00:00:00  2022-08-01 00:00:00
2          C                    1                    1                    1                    1                    1                    1                    1                    1                    1                    0                    0                    0                    0                    0                    0                    0                    0                    0                    0                    0
3          D                    1                    1                    1                    1                    1                    1                    1                    1                    1                    1                    1                    1                    1                    0                    0                    0                    0                    0                    0                    0

我想退回产品最后销售日期的清单。例如，对于产品"C"，它将是"'2021-10-01'"，对于产品"D"，它将是"'2022-02-01'">

我运行for循环，但它返回给我val>0的所有日期。(预计)我怎样才能调整循环，使它只返回最后一个日期?

for col in df.iloc[:,1:].columns:
for val in df[col]:
if val>0:
print(col)

Answer 1

不要循环。用stack重塑并用groupby.max获得每个售出产品的最大日期:

tmp = df.set_index('product').rename_axis(columns='date')
out = (tmp[tmp.eq(1)].stack().reset_index('date')
.groupby('product')['date'].max()
)

输出:

product
C    2021-09-01 00:00:00
D    2022-01-01 00:00:00
Name: date, dtype: object