Changing y-axis to density

By default, you will notice that the y-axis is the 'count' of points that fell within a given bin. This is nice and interpretable, but what if we wanted to interpret the plot as a true density curve like it's trying to estimate? I.e. all the (bar widths) * (bar heights) sum to 1?

To do this we simply add y = stat(density) to the aesthetic mappings, this will re-scale the y-axis from counts to an empirical probability estimate. Note this won't change the shape of the plot at all, but will simply give you a different interpretation of the y-axis.

Let's try it out on the hour of the day that a speeder was pulled over (hour_of_day). In addition, lower the opacity of the bars a bit so the grid lines show through to allow easier comparisons.

set x-aesthetic to hour_of_day.
set the y-aesthetic to stat(density).
change the alpha value in geom_histogram() to 0.8.

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Exercise

Changing y-axis to density

Instructions