按行串联并用公共列值替换 nan

Question

Below is the input data df1

A        B        C          D  E   F   G
Messi   Forward   Argentina  1  Nan 5   6
Ronaldo Defender  Portugal  Nan 4   Nan 3
Messi   Midfield  Argentina Nan 5   Nan 6
Ronaldo Forward   Portugal   3  Nan 2   3
Mbappe  Forward   France    1   3   2   5

Below is the intended output

df

A         B                   C         D   E   F   G
Messi   Forward,Midfield    Argentina   1   5   5   6
Ronaldo Forward,Defender    Portugal    3   4   2   3
Mbappe  Forward               France    1   3   2   5

My try:

df.groupby(['A','C'])['B'].agg(','.join).reset_index()
df.fillna(method='ffill')

Do we have a better way to do this?

Answer 1

You can get first non missing values per groups by all columns without A,C and for B aggregate by join :

d = dict.fromkeys(df.columns.difference(['A','C']), 'first')
d['B'] = ','.join

df1 = df.groupby(['A','C'], sort=False, as_index=False).agg(d)
print (df1)
         A          C                 B    D    E    F  G
0    Messi  Argentina  Forward,Midfield  1.0  5.0  5.0  6
1  Ronaldo   Portugal  Defender,Forward  3.0  4.0  2.0  3
2   Mbappe     France           Forward  1.0  3.0  2.0  5

---

df1 = df.groupby(['A','C'], sort=False, as_index=False).agg(d).convert_dtypes()
print (df1)
         A          C                 B  D  E  F  G
0    Messi  Argentina  Forward,Midfield  1  5  5  6
1  Ronaldo   Portugal  Defender,Forward  3  4  2  3
2   Mbappe     France           Forward  1  3  2  5

Answer 2

For a generic method without manual definition of the columns, you can use the columns types to define whether to aggregate with ', '.join or 'first' :

from pandas.api.types import is_string_dtype

out = (df.groupby(['A', 'C'], as_index=False)
         .agg({c: ', '.join if is_string_dtype(df[c]) else 'first' for c in df})
       )

Output:

                  A                  B                     C    D    E    F  G
0            Mbappe            Forward                France  1.0  3.0  2.0  5
1      Messi, Messi  Forward, Midfield  Argentina, Argentina  1.0  5.0  5.0  6
2  Ronaldo, Ronaldo  Defender, Forward    Portugal, Portugal  3.0  4.0  2.0  3