How to use groupby to concatenate strings in python pandas?

Question

I currently have dataframe at the top. Is there a way to use a groupby function to get another dataframe to group the data and concatenate the words into the format like further below using python pandas?

Thanks

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Answer 1

You can apply join on your column after groupby :

df.groupby('index')['words'].apply(','.join)

Example:

In [326]:
df = pd.DataFrame({'id':['a','a','b','c','c'], 'words':['asd','rtr','s','rrtttt','dsfd']})
df

Out[326]:
  id   words
0  a     asd
1  a     rtr
2  b       s
3  c  rrtttt
4  c    dsfd

In [327]:
df.groupby('id')['words'].apply(','.join)

Out[327]:
id
a        asd,rtr
b              s
c    rrtttt,dsfd
Name: words, dtype: object

Answer 2

If you want to save even more ink, you don't need to use .apply() since .agg() can take a function to apply to each group:

df.groupby('id')['words'].agg(','.join)

OR

# this way you can add multiple columns and different aggregates as needed.
df.groupby('id').agg({'words': ','.join})