Learning R

Appendix D. Solutions to Exercises

Exercise 1-1

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Exercise 1-2

Use the colon operator to create a vector, and the sd function:

sd(0:100)

Exercise 1-3

Type demo(plotmath) and hit Enter, or click the plots to see what’s on offer.

Exercise 2-1

1. Simple division gets the reciprocal, and atan calculates the inverse (arc) tangent:

   atan(1 / 1:1000)

2. Assign variables using <-:

   x <- 1:1000
   y <- atan(1 / x)
   z <- 1 / tan(y)

Exercise 2-2

For comparing two vectors that should contain the same numbers, all.equal is usually what you need:

x == z
identical(x, z)
all.equal(x, z)
all.equal(x, z, tolerance = 0)

Exercise 2-3

The exact values contained in the following three vectors may vary:

true_and_missing <- c(NA, TRUE, NA)
false_and_missing <- c(FALSE, FALSE, NA)
mixed <- c(TRUE, FALSE, NA)

any(true_and_missing)
any(false_and_missing)
any(mixed)
all(true_and_missing)
all(false_and_missing)
all(mixed)

Exercise 3-1

class(Inf)
class(NA)
class(NaN)
class("")

Repeat with typeof, mode, and storage.mode.

Exercise 3-2

pets <- factor(sample(
  c("dog", "cat", "hamster", "goldfish"),
  1000,
  replace = TRUE
))
head(pets)
summary(pets)

Converting to factors is recommended but not compulsory.

Exercise 3-3

carrot <- 1
potato <- 2
swede  <- 3
ls(pattern = "a")

Your vegetables may vary.

Exercise 4-1

There are several possibilities for creating sequences, including the colon operator. This solution uses seq_len and seq_along:

n <- ...