R stuff

Question 1

remove a variable x

Answer 1

rm(x)

Question 2

special constant for:

missing or undefined data

Answer 2

NA

Question 3

special constant for:

empty object

Answer 3

NULL

Question 4

special constant for:

positive / negative infinity?

Answer 4

Inf / -Inf

Question 5

special constant for:

results that cannot be reasonably defined

Answer 5

NaN

(not a number)

Question 6

Check if a number eg x is finite?

Answer 6

is.finite(x)

Question 7

How to combine Values into a Vector or List?

sio

Answer 7

c: Combine Values into a Vector or List

eg

c(1,7:9)
c(1:5, 10.5, “next”)

Question 8

what are the three common tasks that c() can be used for?

What does c stand for?

Answer 8

1. Create a vector.
2. Concatenate multiple vectors.
3. Create columns in a data frame.

c stands for combine

Question 9

Check if something:

• is (not) a number?
• is NULL?

Answer 9

• is.nan()
• is.null()

Question 10

Make a vector that holds true, true, false

Answer 10

• c(TRUE, TRUE, FALSE)
• c(T, T, F)

Question 11

v4 <- c(v1,v2,v3,”boo”)

What type will the elements be?

Answer 11

all strings

Question 12

Make a vector with the numbers from 1 to 7

Answer 12

v <- 1:7 # same as c(1,2,3,4,5,6,7)

Question 13

Make a vector with 0 repeated 77 times

Answer 13

v <- rep(0, 77) # repeat zero 77 times: v is a vector of 77 zeroes

Question 14

Make a vector with the even numbers from 10 to 20

Answer 14

v <- seq(10,20,2) # sequence: numbers between 10 and 20, in jumps of 2

Question 15

Make a vector with 1,2,3,1,2,3

Answer 15

v <- rep(1:3, times=2) # Repeat 1,2,3 twice

Question 16

Make a vector with the numbers 1,1,2,2, … up to 10

Answer 16

v <- rep(1:10, each=2) # Repeat each element twice

Question 17

check the length of vector v?

Answer 17

length(v)

Question 18

How can you add the elements of two vectors together?

Answer 18

eg
v1 <- 1:5 # 1,2,3,4,5
v2 <- rep(1,5) # 1,1,1,1,1

element wise addition:
v1 + v2

Question 19

How can you

• add 1 to each element of a vector v1?
• multiply each element by 2?

Answer 19

• v1 + 1
• v1 * 2

Question 20

Mathematical operations

Consider a vector v. How can you get the

• sum of all elements?
• mean of all elements?
• standard deviation?
• correlation between v and v*5?

Answer 20

• sum(v)
• mean(v)
• sd(v)
• cor(v, v*5)

Question 21

Logical operations - consider vectors v1 and v2:

compare each element in v1 to corresponding elements in v2 / to the number 2, and return a logical vector

Answer 21

v1 < v2 / v1 < 2
v1 > v2
v1 >= v2
…
v1 == v2
v1 != v2

Question 22

Logical operations - consider vectors v1 and v2:

Generate a logical vector which checks if each element in v1 is greater than 2 OR the corresponding element in v2 is greater than 0

Answer 22

(v1>2) | (v2>0) # | is the boolean OR, returns a vector (brackets optional)

If either of the statements are true –> TRUE
if neither is true –> FALSE

Question 23

Logical operations - consider vectors v1 and v2:

Generate a logical vector which checks if each element in v1 is greater than 2 AND the corresponding element in v2 is greater than 0

Answer 23

v1>2 & v2>0
(v1>2) & (v2>0)

Question 24

How do you access the ith element of a vector v?

Answer 24

v[i]

Question 25

How do you access the 2nd, 3rd, and 4th elements of a vector v?

Answer 25

v[2:4]

Question 26

How can you access the 1st and 3rd elements of a vector v (that has 5 elements)?

Answer 26

v[c(1,3)]
v[c(T,F,T,F,F)]

Question 27

Where does indexing start for R?

Answer 27

from 1 !