Exercise

# Data frames and matrices - column selection

All values in a matrix must have the same data type, which has efficiency implications when selecting rows and columns.

Suppose we have two objects, `mat`

(a matrix) and `df`

(a data frame).

Instructions

**100 XP**

Using the `microbenchmark()`

function, how long does it take to select the first column from each of these object? In other words, which is faster `mat[, 1]`

or `df[, 1]`

?