A vector represents a series of variables as opposed to a single variable. We denote a vector with an arrow over the variable. Some authors will instead underline the variable. $\vec x$ Here, $\vec x$ denotes that there are a series of $x_is as in $\vec x = (x_1, x_2, \dots, x_n)$ For example, a [[joint probability density function]] includes the vector of all observed $x_is as in $f(\vec x)$. In R, a vector is created with `c()`. ```R my_vector <- c(1, 2, 3) ```