How to take data from another dataframe based on 2 columns

Question

Here is my code

A['period_id'] = A['period_number','Session'].map(B.set_index(['period_number','Session'])['period_id'])

So I want to take data from column period_id of B to give to A, based on criteria that 2 columns ( period_number and Session ) are matched. However it gave me error. What can I do?

Answer 1

You can use pd.merge :

A_columns = A.columns
A_columns.append("period_id")

# merge based on period_number and Session
merged_df = pd.merge(A, B,  how='left', left_on=['period_number','Session'], right_on = ['period_number','Session'])

final_df = merged_df[A_columns] # filter for only columns in A + `period_id` from B

Note that if A 's column names are different for period_number and Session , you'll have to adjust your left_on , and vice versa for B . To be explicit A is the left dataframe here, and B is the right dataframe.