Keep the value corresponding to the maximum of another column in a dataframe

Question

I have a DataFrame

    day  type  price
0  10900     2    300
1  10900     1    500
2  10900     3    200
3  10901     5    100
4  10901     2    400
5  10901     1    300
6  10902     2    100
7  10902     3    300
8  10902     1    200
9  10902     4    400

and i want for each day to keep the price of the highest type and replicated on all the prices of that day so the result will be:

 day  type  price
0  10900     2    200
1  10900     1    200
2  10900     3    200
3  10901     5    100
4  10901     2    100
5  10901     1    100
6  10902     2    400
7  10902     3    400
8  10902     1    400
9  10902     4    400

so this is what i am doing and i am wondering if it is the best way or if there is a way to not use the merge and make the group by in another way:

tmp_df=df[df.groupby('day')['type'].transform('max') == df['type']].reset_index()
df=df[['day','type']].merge(tmp_df[['day','price']],on='day')

Answer 1

df["price"] = df.groupby("day", as_index=False)["price"].transform(
    lambda x: df.loc[df.loc[x.index, "type"].idxmax(), "price"]
)
print(df)

Prints:

     day  type  price
0  10900     2    200
1  10900     1    200
2  10900     3    200
3  10901     5    100
4  10901     2    100
5  10901     1    100
6  10902     2    400
7  10902     3    400
8  10902     1    400
9  10902     4    400