This homework is due on Feb. 29, 2024 at 11:00pm. Please submit as a pdf file on Canvas.

In this homework, we will work with the ufo_sightings dataset:

head(ufo_sightings)

The main columns we will use are year (the year of the sighting), city (the city in which the sighting was reported), and state (the state in which the sighting was reported).

Problem 1: (8 pts) Since 1980 (inclusive), what are the top 15 cities that have reported the most UFO sightings? Create a new dataframe to answer the question. No plots are necessary.

(Hint: You can use slice(1:15) to select the first fifteen rows in a data frame.)

# your code here

Problem 2: (8 pts)

Next, how has the number of UFO sightings changed for five states since 1970? Please follow these steps:

1. Filter the dataset to keep the following five states: CA, NY, TX, AZ, ID
2. Keep only the records from 1970 and onwards.
3. Find the number of records for each year and state.
4. Output the new table below your code block.

Your final table should be in long format and have three columns, year, state, and count. You will plot this table in Problem 3.

# your code here

Problem 3: (4 pts)

Use the new dataframe you made in Problem 2 and add an appropriate color scale from the colorspace package to the plot below.

your_dataframe_here %>% # use the dataframe from Problem 2 here, and set eval = TRUE in the chunk header
ggplot(aes(x = year, y = count, color = state)) +
geom_line() +
xlab("Year") +
ylab("UFO Sightings (Count)") +
theme_bw()