Transposing planet data

You're again working on a planet dataset derived from the devstronomy project. This time, you're interested in the correlation between the diameter of a planet and the number of moons circling it.

However, the dataset (planet_df) has a row for each variable and a column for each planet (observation). You'll transpose this data in two steps and then create a plot to inspect the correlation.

The ggplot2 package has been pre-loaded for you.