pandas：基于另一个datafram中的行值计数的转换

Question

我有两个数据帧：

df1型：

Gender  Registered
female  1
male    0
female  0
female  1
male    1
male    0

df2型：

Gender
female
female
male
male

我想修改df2，这样就有了一个新的列'Count'，它的Count为registered=1，对应于df1中的gender值。例如，在df1中有2名注册女性和1名注册男性。我想将df2转换为如下输出：

输出：

Gender  Count
female  2
female  2
male    1
male    1

我尝试了很多方法，但都没有成功。你知道吗

Answer 1

sum+map：

v = df1.groupby('Gender').Registered.sum()
df2.assign(Count=df2.Gender.map(v))

   Gender  Count
0  female      2
1  female      2
2    male      1
3    male      1

Answer 2

pd.merge

pd.merge(df2, df1.groupby('Gender', as_index=False).sum())

    Gender  Registered
0   female  2
1   female  2
2   male    1
3   male    1