在另一列的值的总和中添加一个新列

Question

所以我使用熊猫，并试图在“总计”中添加一个新的列，它是当年所有车辆数量的总和。你知道吗

由此：

    type            year     number

Private cars        2005    401638
Motorcycles         2005    138588
Off peak cars       2005    12947
Motorcycles         2005    846

对这样的事情：

 type            year       number       Total

Private cars        2005    401638      554019
Motorcycles         2005    138588
Off peak cars       2005    12947
Motorcycles         2005    846

Answer 1

这提供了一个类似的数据帧：

total = df['numer'].sum()
df['Total'] = np.ones_line(df['number'].values) * total

Answer 2

使用GroupBy+transform和sum：

df['Year_Total'] = df.groupby('year')['number'].transform('sum')

请注意，这将为您提供每行的年度总数。如果您希望“清空”某些行的总计，那么应该精确地指定其逻辑。你知道吗

Answer 3

使用^{}，然后在必要时替换重复的值：

df['Total'] = df.groupby('year')['number'].transform('sum')
print (df)
            type  year  number  Total
0   Private cars  2005       1      3
1    Motorcycles  2005       2      3
2  Off peak cars  2006       5     20
3    Motorcycles  2006       7     20
4   Motorcycles1  2006       8     20

df.loc[df['year'].duplicated(), 'Total'] = np.nan
print (df)
            type  year  number  Total
0   Private cars  2005       1    3.0
1    Motorcycles  2005       2    NaN
2  Off peak cars  2006       5   20.0
3    Motorcycles  2006       7    NaN
4   Motorcycles1  2006       8    NaN

可以替换为空值，但不建议这样做，因为使用字符串获取混合值，某些函数应失败：

df.loc[df['year'].duplicated(), 'Total'] = ''
print (df)
            type  year  number Total
0   Private cars  2005       1     3
1    Motorcycles  2005       2      
2  Off peak cars  2006       5    20
3    Motorcycles  2006       7      
4   Motorcycles1  2006       8