pandas check if there are duplicates of repeated values between the two columns and not inside one column

Question

I have 2 columns and I want to check if there are duplicates of repeated values between the two columns and not inside one column. The length of the datasets is not equal. I am using

df2['columnA'] = df1['columnA'].isin(df2['columnA'])

but it gives me the wrong answer.

I want to check if there are repeated values from the longer dataset in the shorter dataset. if yes I want a column to be added to the shorter dataset, indicating True. If not False

Dataset1:

columnA

1598618777
553834731
1562313985
1138106620
1463509237
1560632350

Dataset2

ColumnA

1330011201
1464235676
1232080731
1446254576
1563383895
1402595440
1555409735
1551787372
1523820531
1138106620
1196764367
1551787372

Answer 1

you can create one dataframe with append and then use duplicated to check the duplicate and if you want to remove then you can use .drop_duplicates

df=Dataset1.append(Dataset1)
df.duplicated(subset=['ColumnA'])