Check the documentation on the mean$()$ function again:

$?$mean

The Usage section of the documentation includes two versions of the mean$()$ function. The first usage,

mean$($x$,...)$

is the most general usage of the mean function. The 'Default S$3$ method', however, is:

mean$($x$,$ trim $=0,$ na$.$rm $=$ FALSE, $...)$

The $...$ is called the ellipsis. It is a way for R to pass arguments along without the function having to name them explicitly. The ellipsis will be treated in more detail in future courses.

For the remainder of this exercise, just work with the second usage of the mean function. Notice that both trim and na$.$rm have default values. This makes them optional arguments.

Instructions

$100$ XP

Calculate the mean of the element$-$wise sum of linkedin and facebook and store the result in a variable avg$\_$sum.

Calculate the mean once more, but this time set the trim argument equal to $0\mathrm{.}2$ and assign the result to avg$\_$sum$\_$trimmed.

Print out both avg$\_$sum and avg$\_$sum$\_$trimmed; can you spot the difference?