# Exercise: The weekly shop
# https://hands-on-computer-science.de/ds/en/items/r-exercise-shopping/
#
# The task and the hints are comments here; the solution is on the page.

# Task ----
#
# A receipt lists six items. For each you know the price per piece and the
# amount, only the price of the cheese is illegible:
# | Item | Price per piece | Amount |
# |---|---|---|
# | Milk | 1.09 | 3 |
# | Oat drink | 1.79 | 2 |
# | Bread | 2.49 | 1 |
# | Cheese | illegible | 1 |
# | Apples | 0.45 | 6 |
# | Chocolate | 1.29 | 2 |
#
# Answer three questions with R, each in a box of its own:
# 1. What does the shopping cost without the cheese?
# 2. How many items cost more than 1.50 euros per piece?
# 3. What share of the known total do milk and oat drink make up together?

# Your code ----
#

items <- c("milk", "oat drink", "bread", "cheese", "apples", "chocolate")
prices <- c(1.09, 1.79, 2.49, NA, 0.45, 1.29)
amounts <- c(3, 2, 1, 1, 6, 2)

# 1. total without the cheese

# 2. items above 1.50 euros

# 3. share of milk and oat drink

# Hint:
# `prices * amounts` gives the amount per line of the receipt. For the cheese
# it says `NA`, which is why `sum()` needs a particular argument. To check: the
# known amount is 14.62 euros.

# Hint:
# For the second question you count a comparison with `sum()`. The missing
# price of the cheese is in the way here too. For the third you select the two
# drinks with `%in%` and divide their amount by the known total.

# For the quick ones ----
#
# The cheese cost 3.99 euros. Fill in the price: which of your answers change,
# and which lines of your code do you have to touch for that?