We are going to use the sample function to create such a vector.
As its name implied, the function samples among a set it is provided as input.
It is as such important to provide a set in integers. As explained in
?sample, if given a single numeric input n, sample will sample n values
from 1:n without replacement (replacement = FALSE), resulting in a permutation of 1:n.
Using n equal 20 and making sure that 1:20 produces a sequence of integers
class(1:20)## [1] "integer"
we can now produce our vector of integers i:
i <- sample(20)
i## [1] 2 7 5 17 14 10 15 1 12 13 6 9 18 11 16 3 19 20 4 8
typeof(i)## [1] "integer"
The runif(n) function samples n values from a uniform distribution ranging (by default) from 0 to 1.
d <- runif(20)
d## [1] 0.43514 0.28883 0.87758 0.08802 0.32376 0.15818 0.76988 0.51394
## [9] 0.93103 0.14682 0.62064 0.34712 0.40829 0.44959 0.80837 0.78791
## [17] 0.16037 0.28768 0.79473 0.48247
typeof(d)## [1] "double"
We could also have used rnorm to sample values from a normal distribution.
typeof(rnorm(20))## [1] "double"
Instead of typing the sequence of characters ourselves, we will use the
built-in variable letters, which stores the 26 letters from the alphabet.
We will select the letters at positions 1 to 20 in the order defined by i.
head(letters)## [1] "a" "b" "c" "d" "e" "f"
s <- letters[i]
s## [1] "b" "g" "e" "q" "n" "j" "o" "a" "l" "m" "f" "i" "r" "k" "p" "c" "s"
## [18] "t" "d" "h"
typeof(s)## [1] "character"
length(s)## [1] 20
Other built-in variables of interest are LETTERS (as letters, but capital letters),
month.name (month names), pi, ... see ?letters.
Although TRUE is a perfectly valid vector of logicals (of length 1), we are going to use
a comparison operator on the vector i to create a vector of logicals
(see ?'==' or help("<") for details).
Each element of i will be used in turn and compared to the second operand (10 below),
effectively resulting in a vector of logicals of the same length than i.
l <- i >= 10
## same as
l <- (i >= 10)
l## [1] FALSE FALSE FALSE TRUE TRUE TRUE TRUE FALSE TRUE TRUE FALSE
## [12] FALSE TRUE TRUE TRUE FALSE TRUE TRUE FALSE FALSE
typeof(l)## [1] "logical"
length(i)## [1] 20
length(l)## [1] 20