Python unique concatenate value of a column in another

Question

I'm trying to perform this process, imagine to have the following and I want to obtain col4. :

Col1	Col2	Col3	Col 4	Col 5
SF	123	QW	QW, BF	1
SF	456	AF	AF	2
SO	xxx	AF	AF, BF	3
SO	yyy	GD	GD	4
SF	123	BF	QW, BF	1
RE	xxx	BF	AF, BF	5

For the purpose of aggragation I'm using these 2 lines of code:

df[df['col1']!='SF'].groupby(['Col2']).agg({'Col3' : lambda x: ','.join(x.unique())})

df[df['col1']=='SF'].groupby(['Col2','Col5']).agg({'Col3':','.join})

But I don't know how to put them on df. I tried also a merge but didn't work. I only hope to have been clear!!

Thanks so much in advance

EDIT 1 Sorry for not being clear. Before to perform any line of code I have Col1, Col2, Col3, Col5. Col4 is the output I would like to obtain.

Which columns do you already have? And which do you want to add? — not_speshal
– not_speshal, Commented Oct 4, 2021 at 17:23

not_speshal · Accepted Answer · 2021-10-04 17:27:10Z

2

You transform instead of agg to assign back to the original DataFrame:

df["Col4"] = df.groupby("Col2")["Col3"].transform(lambda x: ", ".join(x.unique()))

answered Oct 4, 2021 at 17:27

not_speshal

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1 Comment

Frisk19 Over a year ago

It returns with an error: "Length mismatch: Expected axis has 133028 elements, new values have 133243 elements". I I was thinking to rewrite the question and publish another one, since I could be clearer explaining the issue

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