вставлять данные с использованием GroupBy и Transform
import pandas as pd
from datetime import datetime
def generate_data():
...
t = datetime.now()
df = generate_data()
df['value'] = df.groupby(['category', 'name'])['value']\
.transform(lambda x: x.fillna(x.mean()))
print(datetime.now()-t)
# 0:00:00.016012
t = datetime.now()
df = generate_data()
df["value"] = df.groupby(['category', 'name'])\
.transform(lambda x: x.fillna(x.mean()))['value']
print(datetime.now()-t)
# 0:00:00.030022
Filthy Flatworm