extract() simply uses a
for loop to extract the nth element
from each vector in a list. However, it can also operate on a data frame.
This is equivalent to taking the first element of each vector and making a
those elements the first vector in a new list, and it continues on so until
it reaches the last element.
A list of vectors of equal length, a data frame, or a matrix.
If the length of the smallest vector in
A number (preferably the length of the vectors) to create a