Apples oranges

# Table: Sales
# 
# +---------------+---------+
# | Column Name   | Type    |
# +---------------+---------+
# | sale_date     | date    |
# | fruit         | enum    |
# | sold_num      | int     |
# +---------------+---------+
# (sale_date, fruit) is the primary key (combination of columns with unique values) of this table.
# This table contains the sales of "apples" and "oranges" sold each day.
# 
#  
# 
# Write a solution to report the difference between the number of apples and oranges sold each day.
# 
# Return the result table ordered by sale_date.
# 
# The result format is in the following example.
#
# Example 1:
# Input:
# Sales table:
# +------------+------------+-------------+
# | sale_date  | fruit      | sold_num    |
# +------------+------------+-------------+
# | 2020-05-01 | apples     | 10          |
# | 2020-05-01 | oranges    | 8           |
# | 2020-05-02 | apples     | 15          |
# | 2020-05-02 | oranges    | 15          |
# | 2020-05-03 | apples     | 20          |
# | 2020-05-03 | oranges    | 0           |
# | 2020-05-04 | apples     | 15          |
# | 2020-05-04 | oranges    | 16          |
# +------------+------------+-------------+
# Output:
# +------------+--------------+
# | sale_date  | diff         |
# +------------+--------------+
# | 2020-05-01 | 2            |
# | 2020-05-02 | 0            |
# | 2020-05-03 | 20           |
# | 2020-05-04 | -1           |
# +------------+--------------+
# Explanation:
# Day 2020-05-01, 10 apples and 8 oranges were sold (Difference  10 - 8 = 2).
# Day 2020-05-02, 15 apples and 15 oranges were sold (Difference 15 - 15 = 0).
# Day 2020-05-03, 20 apples and 0 oranges were sold (Difference 20 - 0 = 20).
# Day 2020-05-04, 15 apples and 16 oranges were sold (Difference 15 - 16 = -1).

import pandas as pd

def apples_oranges(sales: pd.DataFrame) -> pd.DataFrame:
  apples = sales[sales['fruit'] == 'apples'].set_index('sale_date')['sold_num']
  oranges = sales[sales['fruit'] == 'oranges'].set_index('sale_date')['sold_num']
  diff = (apples - oranges).reset_index()
  diff.columns = ['sale_date', 'diff']
  return diff.sort_values('sale_date')