Answers for "apply using two columns pandas"

plotting two columns of a dataframe in python

df.plot(x='col_name_1', y='col_name_2', style='o')

pandas merge two columns from different dataframes

#suppose you have two dataframes df1 and df2, and 
#you need to merge them along the column id
df_merge_col = pd.merge(df1, df2, on='id')