Python - Pandas 過濾器和分組依據

首先Series.mode按原始列比較每個組，過濾器，並在必要時添加未過濾的行，分配bin給cluster-2：

print (df)
  file  cluster-1  cluster-2
0    A          1          2
1    D          1          2
2    G          2          4
3    B          3          1
4    E          3          2
5    J          3          1

m = (df.groupby('cluster-1')['cluster-2']
      .transform(lambda x: x.mode().iat[0])
      .eq(df['cluster-2']))
df = (df[m].append(df[~m].assign(**{'cluster-1':'bin'}), ignore_index=True)
          .rename(columns={'cluster-1':'cluster'})
          .drop('cluster-2', axis=1))
print (df)
  file cluster
0    A       1
1    D       1
2    G       2
3    B       3
4    J       3
5    E     bin