How to concat two Pandas dataframes that have the same columns but only if the value of one column i-CodePudding

I have two dataframes like the below:

DF1:

col1	col2
22	yes
22	no
24	yes
22	no
27	no

DF2:

col1	col2
28	yes
22	no
29	yes
22	yes
27	yes

I want to concat both dataframes, so that I end up with the below. I don't want to join the dataframes on col1, as that doubles the number of columns. I just want to combine the dataframe vertically if they share a common value on "col1." Any help on this?

DF3:

col1	col2
22	yes
22	no
22	no
22	no
22	yes
27	no
27	yes

CodePudding user response：

Let us first find the common values using set intersection then concat the required rows from df1 and df2 and optionally sort the values

i = set(df1['col1']) & set(df2['col1'])
pd.concat([df1[df1['col1'].isin(i)], df2[df2['col1'].isin(i)]]).sort_values('col1')

   col1 col2
0    22  yes
1    22   no
3    22   no
1    22   no
3    22  yes
4    27   no
4    27  yes