def left_join(left, right, left_vars, right_vars):
 indices = left_join_indices(left, right, left_vars, right_vars)
 return join_table_by_indices(left, right, indices)

def left_join ( left , right , left_vars , right_vars ) : indices = left_join_indices ( left , right , left_vars , right_vars ) return join_table_by_indices ( left , right , indices )
left join left and right on values of left/right_vars .