Python df 按日期添加行，因此每个组都在同一日期结束。填充剩余的行

Question

为了使用地理绘图动画帧，我希望我的所有组都在同一天结束。这将避免最后一帧使某些国家变灰。目前，根据日期的最新数据点是 'Timestamp('2021-05-13 00:00:00')'。

因此，在下一步中，我想根据所有国家/地区添加新行，以便它们在 df 中有直到最新日期的行。可以使用 ffill 填充列 'people_vaccinated_per_hundred' 和 'people_fully_vaccinated_per_hundred'。

数据：

理想情况下，如果挪威比最新数据点“2021-05-13”少 1 天，那么它应该添加一个新行，如下所示。这应该对 df 中的所有其他国家/地区完成。

例子

    country iso_code    date    people_vaccinated_per_hundred   people_fully_vaccinated_per_hundred
12028   Norway  NOR 2021-05-02  0.00    NaN
12029   Norway  NOR 2021-05-03  0.00    NaN
12188   Norway  NOR ...         ...     ...
12188   Norway  NOR 2021-05-11  27.81   9.55
12189   Norway  NOR 2021-05-12  28.49   10.42

Add new row
12189   Norway  NOR 2021-05-13  28.49   10.42

Answer 1

一个直截了当的方法可能是创建国家和日期的笛卡尔积，然后加入这个为每个缺失的日期和国家组合创建空值。

countries = df.loc[:, ['country', 'iso_code']].drop_duplicates()
dates = df.loc[:, 'date'].drop_duplicates()
all_countries_dates = countries.merge(dates, how='cross')

df.merge(all_countries_dates, how='right', on=['country', 'iso_code', 'date'])

数据集如下：

country       iso_code  date        people_vaccinated   people_fully_vaccinated
Norway        NOR       2021-05-09  0.00                1.00
Norway        NOR       2021-05-10  0.00                3.00
Norway        NOR       2021-05-11  27.81               9.55
Norway        NOR       2021-05-12  28.49               10.42
Norway        NOR       2021-05-13  28.49               10.42
United States USA       2021-05-09  23.00               3.00
United States USA       2021-05-10  23.00               3.00

这个转换会给你：

country       iso_code  date        people_vaccinated   people_fully_vaccinated
Norway        NOR       2021-05-09  0.00                1.00
Norway        NOR       2021-05-10  0.00                3.00
Norway        NOR       2021-05-11  27.81               9.55
Norway        NOR       2021-05-12  28.49               10.42
Norway        NOR       2021-05-13  28.49               10.42
United States USA       2021-05-09  23.00               3.00
United States USA       2021-05-10  23.00               3.00
United States USA       2021-05-11  NaN                 NaN
United States USA       2021-05-12  NaN                 NaN
United States USA       2021-05-13  NaN                 NaN

在此之后，您可以使用 fillna 更改添加行的空值。

Answer 2

早于 pandas 1.1.5

版本的交叉连接代码

#creating a df with all unique countries and iso_codes
#creating a new table with all the dates in the original dataframe
countries = animation_covid_df.loc[:, ['country', 'iso_code']].drop_duplicates()
dates_df = animation_covid_df.loc[:, ['date']].drop_duplicates()

#creating an index called row number to later merge the dates table with the countries table on
dates_df['row_number'] = dates_df.reset_index().index

number_of_dates = dates_df.max() #shows the number of dates or rows in the the dates table

#creating an equivalent number of rows for each country as there are dates in the dates_df 
indexed_country = countries.append([countries]*number_of_dates[1],ignore_index=True)
indexed_country = indexed_country.sort_values(['country', 'iso_code'], ascending=True)
#creating a new column called 'row_number' to join the indexed_country df with the dates_df
indexed_country['row_number'] = indexed_country.groupby(['country', 'iso_code']).cumcount()+1

#merging all the indexed countries with all the possible dates on the row number
indexed_country_date_df = indexed_country.merge(dates_df, on='row_number', how='left', suffixes=('_1', '_2'))

#setting the 'date' column in both tables to datetime so they can be merged on
animation_covid_df['date'] = pd.to_datetime(animation_covid_df['date'])
indexed_country_date_df['date'] = pd.to_datetime(indexed_country_date_df['date'])

Python df 按日期添加行，因此每个组都在同一日期结束。填充剩余的行

Python df add rows by date, so each group ends on the same date. Ffill remaining rows

python

pandas

group-by

row

ffill