Chapter 1 - Introduction to R

Question 1

Exponential/Log functions

Answer 1

exp(…) and log(x, base)

Question 2

Install a package and load

Answer 2

install.packages(‘…’), library(package)

Question 3

Scatter plot

Answer 3

plot(X,Y)

Question 4

Histogram

Answer 4

hist(X)

Question 5

Make a vector

Answer 5

x <- c(…)

Question 6

Sum, Mean, Standard dev, length of a vector?

Answer 6

sum(), mean(), sd(), length()

Question 7

Multiple plots at once? 1 row 2 col? 2 row 1 col?

Answer 7

par(mfrow = c(1,2)) and par(mfrow = c(2,1))

Question 8

Make lines in a plot

Answer 8

lines(X,Y)

Question 9

What order does R upcast to for vectors?

Answer 9

Boolean -> Numeric -> String

Question 10

Check object types for numeric, factor, logical, and character.

Answer 10

as.”type”

Question 11

Print a string without quotations.

Answer 11

cat(…)

Question 12

Count the number of characters in a string.

Answer 12

nchar(a)

Question 13

Character translation function

Answer 13

chartr(old, new, string)

Question 14

Make a string upper case, lower case?

Answer 14

toupper(a), tolower(a)

Question 15

Get a sub-string.

Answer 15

substr(beg,end,string)

Question 16

Paste function

Answer 16

paste(a,b,sep = “”, collapse = “”)

Question 17

Split a string

Answer 17

strsplit(a, split = “”)

Question 18

Combine two vectors into one

Answer 18

c(a,b)

Question 19

Make columns in a regular vector

Answer 19

c(‘name’ = c(…))

Question 20

Make a sequence of numbers in R

Answer 20

seq(start,end,step) or a:b (for integers)

Question 21

Repeat a vector

Answer 21

rep(x, integer for repeating the whole vector)
rep(x, vector for times of each item)
rep(x, each = a)

Question 22

Make a matrix

Answer 22

x <- c(…); dim(x) <- c(row,col)
or
matrix(x,nrow, ncol, byrow, bycol)

Question 23

Adjust the dimension names of a matrix.

Answer 23

rownames(x) <- c(…)
colnames(x) <- c(…)
names(dimnames(x)) <- c(…)

Question 24

Combine columns and rows for two vecotrs/matrix

Answer 24

Example
cbind(A = 1:3, B = 4:6, C = 7:9)
rbind(A = 1:4, B = 4:6, C = 7:9)

Question 25

Factors/Categorical Data in R

Answer 25

factor(data, levels = c(…))
or
factor(data); levels(data) <- c(…)

Question 26

Make a list

Answer 26

mylist <- list(before = intake.pre, after = intake.post)

Question 27

Index a list, with conditions?

Answer 27

mylist$column
mylist$column[index]
mylist$column[condition]

Question 28

Index a vector, with conditions?

Answer 28

x[condition]
x[index]

Question 29

Make a dataframe

Answer 29

data <- data.frame(col1,col2,…)

Question 30

Index a data frame, with conditions?

Answer 30

data[row,col]

Generally with conditioning data frames it looks like this, can be changed.
row cond col cond
data[data$col ==|%<>, c(…)]

Question 31

Check if a vector/item is inside another vector?

Answer 31

%in%