Pandas groupby with delimiter join

Question

I tried to use groupby to group rows with multiple values.

col val
A  Cat
A  Tiger
B  Ball
B  Bat

import pandas as pd
df = pd.read_csv("Inputfile.txt", sep='\t')
group = df.groupby(['col'])['val'].sum()

I got

A CatTiger
B BallBat

I want to introduce a delimiter, so that my output looks like

A Cat-Tiger
B Ball-Bat

I tried,

group = df.groupby(['col'])['val'].sum().apply(lambda x: '-'.join(x))

this yielded,

A C-a-t-T-i-g-e-r
B B-a-l-l-B-a-t

What is the issue here ?

Thanks,

AP

Answer 1

Alternatively you can do it this way:

In [48]: df.groupby('col')['val'].agg('-'.join)
Out[48]:
col
A    Cat-Tiger
B     Ball-Bat
Name: val, dtype: object

---

UPDATE: answering question from the comment:

In [2]: df
Out[2]:
  col    val
0   A    Cat
1   A  Tiger
2   A  Panda
3   B   Ball
4   B    Bat
5   B  Mouse
6   B    Egg

In [3]: df.groupby('col')['val'].agg('-'.join)
Out[3]:
col
A       Cat-Tiger-Panda
B    Ball-Bat-Mouse-Egg
Name: val, dtype: object

Last for convert index or MultiIndex to columns:

df1 = df.groupby('col')['val'].agg('-'.join).reset_index(name='new')

Answer 2

just try

group = df.groupby(['col'])['val'].apply(lambda x: '-'.join(x))

Answer 3

You can first aggregate to list and then join with str.join:

df = pd.DataFrame({'A': [1, 1, 1, 2, 2, 2], 'B': ['a', 'b', 'c', 'd', 'e', 'f']})

df.groupby('A')['B'].agg(list).str.join('-')

Output:

A
1    a-b-c
2    d-e-f
Name: B, dtype: object