Answers for "concatenate columns pandas dataframe"

combining 2 dataframes pandas

df_3 = pd.concat([df_1, df_2])

pandas left join

df.merge(df2, left_on = "doc_id", right_on = "doc_num", how = "left")

dataframe concatenate

# Pandas for Python

df['col1 & col2'] = df['col1']+df['col2']

#Output
#col1	col2	col1 & col2
#A1		A2		A1A2
#B1		B2		B1B2