How can I merge Pandas DF and maintain merged structure?

Question

I'm not quite sure how to explain my problem so I'll just describe it.

DF1
      Name  Year
0   foo  2020
1   bar  2020
2   foo  2019
3   foo  2018

DF2
Name Value
foo  A
bar  A
bar  B

When I merge it, I want:

      Name  Year Value
  foo  2020  A
  bar  2020  A
  bar  2020  B
  foo  2019  A
  foo  2018  A

Basically, if df2 has multiple entries for a value(in this case bar then it should create two entries for it).

Right now I'm just getting one result per row by doing this:

df1['value']=df1[['Name']].merge(df2,how='right').value

This is more or less a duplicate of [Pandas Merging 101](https://stackoverflow.com/q/53645882/7758804). — Trenton McKinney, Feb 03 '21 at 21:01

score 3 · Accepted Answer · answered Feb 03 '21 at 20:54

3

I think you mean how='left' not how='right':

df1.merge(df2, on='Name', how='left')

Output:

  Name  Year Value
0  foo  2020     A
1  bar  2020     A
2  bar  2020     B
3  foo  2019     A
4  foo  2018     A

answered Feb 03 '21 at 20:54

Quang Hoang

I'm sorry I should have mentioned, I tried both - the shape of my DF remained the same for both – Lostsoul Feb 03 '21 at 20:57
2

`mege` returns a new dataframe, you need to reassign. So `df1 = df1.merge(...)`? – Quang Hoang Feb 03 '21 at 20:58

1 Answers1