The R book: Essentials of the R Language

Question 1

logs with base 10

Answer 1

log10()

Question 2

Enter the numbers from the keyboard one at a time

Answer 2

scan()

Question 3

Named Elements within vectors

Answer 3

names(counts) <- 0:8

Question 4

pmax?

Answer 4

vector, of length equal to the longest of x, y, z, containing the maximum of x, y or z for the ith position in each

Question 5

if names(data) is “Growth.rate” “Water” “Detergent” “Dephnia”, how to find the mean growth rate for each detergent

Answer 5

tapply(Growth.rate, Detergent, mean)

Question 6

Calculate the median growth rate for water type and daphnia clone

Answer 6

tapply(Growth.rate, list(Water, Daphnia), median)

Question 7

with function

Answer 7

evaluates an R expression in an environment constructed from data.

Question 8

To see the names of the dataframes in the build-in package called datasets

Answer 8

data()

Question 9

See all available data sets (including those in the installed packages)

Answer 9

data(package = .packages(all.available = TRUE))

Question 10

subscripts on lists

Answer 10

double square

Question 11

reverse sort on vector x

Answer 11

rev(sort(x))

Question 12

Subscripts for values bigger than 5

Answer 12

which(y>5)

Question 13

Every 25th value in a 100-long vector of normal random number with mean value 100 and standard deviation 10

Answer 13

xv <- rnorm(1000, 100, 10)

xv[seq(25, length(xv),25)]

Question 14

Find logical combinations of &

Answer 14

outer(x, x, “&”)

Question 15

repeat function

Answer 15

rep(1:4, each = 2, times = 3)

Question 16

one 1, two 2s, three 3s, and four 4s

Answer 16

rep(1:4, 1:4)

Question 17

Syntamx of gl (‘generate levels’)

Answer 17

gl(‘up to’, ‘with repeats of’, ‘to total length’)

Question 18

Text for the factors levels, rather than numbers

Answer 18

gl(3, 2, 24, labels = c(“A”, “B”, “C”))

Question 19

Create a sequence with the same length as vector x

Answer 19

seq(88, 50, along = x)

Question 20

sequence(c(5, 2, 4))

Answer 20

1 2 3 4 5 1 2 1 2 3 4