Python:如何在不聚合数据帧的情况下进行分组和计数

Question

我的数据框如下所示:

现在我想按列['name', 'grade']分组，并执行count()，结果如下所示:

df.groupby(['姓名', '成绩'], as_index=False).count()

但我想要的应该是这样的:

Answer 1

尝试使用转换:

dict = {"year": [2010, 2011, 2012, 2010, 2011],
   "name": ["kelly", "kelly", "kelly", "peter", "peter"],
   "grade": ["A", "A", "C", "B", "B"] }

import pandas as pd
df = pd.DataFrame(dict)
print(df)

grp = df.groupby(['name', 'grade'], as_index=False)
print(grp.count())

df['count'] = grp['year'].transform('count')
print(df)

PS:记入https://stackoverflow.com/a/41925722/1681985