Objects - the building blocks of R

R For SAS Users

Melinda Higgins, PhD

Research Professor/Senior Biostatistician Emory University

Objects are the building blocks of R

• Everything in R is an object
• Single values (scalars)
• Vectors
• Matrices
• Datasets
• Output from functions

Work with single elements

• Create object x
• Assign value of 4 to x
• View contents of x
• [1] indicates x has 1 element
• Create y as square of x
• View result, type y

x <- 4

x

[1] 4

y <- x * x

y

[1] 16

Other types of elements

• Assign the word "fish" to y
• Assign the logical value FALSE to z
• View y and z

y <- "fish"

z <- FALSE

y
z

[1] "fish"

[1] FALSE

Combine single elements into a vector

# Combine three numbers
c(5, 3, 2)

Combine single elements into a vector

# Assign numeric vector to x
x <- c(5, 3, 2)

# View result
x

Result

[1] 5 3 2

Create vector of character elements

# Add word child into character vector
y <- c("child")

Create vector of character elements

# Add second word young
y <- c("child", "young")

Create vector of character elements

# Add third word old
y <- c("child", "young", "old")

# View y
y

Result

[1] "child" "young" "old"

Create vector of logical elements

# Add TRUE into logical vector
z <- c(TRUE)

• First element is TRUE
• No double quotes needed
• Logical elements are TRUE or FALSE
• ALL CAPS must be used
• T and F may also be used

Create vector of logical elements

# Add FALSE as second element
z <- c(TRUE, FALSE)

Create vector of logical elements

# Add third element TRUE
z <- c(TRUE, FALSE, TRUE)

# View z
z

Result

[1]  TRUE FALSE TRUE

Create matrix from vectors

#  Create numeric vector a
a <- c(5.0, 3.1, 2.4)

• Matrix created from vectors
• Vectors must be same type and length

Create matrix from vectors

#  Create numeric vector a
a <- c(5.0, 3.1, 2.4)

#  Create numeric vector b
b <- c(4.1, 2.2, 5.4)

Create matrix from vectors

# Make m from a,b with 3 rows 2 columns
m <- matrix(c(a, b),
            nrow = 3,
            ncol = 2)

# View m
m

          [,1] [,2]
     [1,]  5.0  4.1
     [2,]  3.1  2.2
     [3,]  2.4  5.4

Create data frame from vectors

# Create numeric variable score
score <- c(5.0, 3.1, 2.4)

# View score
score

     5.0 3.1 2.4

• Data frames created from vectors
• Vectors must be same length
• Vectors can be different types

Create data frame from vectors

# Create character variable age
age <- c("child","young","old")

# View age
age

     "child" "young" "old"

Create data frame from vectors

# Create logical variable test
test <- c(TRUE, FALSE, TRUE)

# View test
test

     TRUE FALSE TRUE

Create data frame from vectors

# Combine to create data frame
d <- data.frame(score, age, test)

# View data frame
d

     score   age  test
       5.0 child  TRUE
       3.1 young FALSE
       2.4   old  TRUE

Determine object type

• Create numeric vector x
• Determine the class of x
• Look at structure str of x

x <- c(5, 3, 2)
class(x)

 [1] "numeric"

str(x)

 num [1:3] 5 3 2

Determine object type

• Character vector y; logical vector z
• Determine the class of y and z
• Look at structure str of y and z

str(y)

 chr [1:3] "child" "young" "old"

str(z)

 logi [1:3] TRUE FALSE TRUE

y <- c("child","young","old")
z <- c(TRUE, FALSE, TRUE)

class(y)

 [1] "character"

class(z)

 [1] "logical"

Determine object type

• Make matrix m
• Get class of m
• See structure str of m

str(m)

 num [1:3, 1:2] 5 3.1 2.4 4.1 2.2 5.4

a <- c(5.0, 3.1, 2.4)
b <- c(4.1, 2.2, 5.4)
m <- matrix(c(a, b),
            nrow = 3,
            ncol = 2)

class(m)

 [1] "matrix"

Determine object type

• Create data.frame d
• Get class of d
• See structure str of d

str(d)

'data.frame':    3 obs. of 3 variables:
 $ score: num  5 3.1 2.4
 $ age  : Factor w/ 3 levels
         "child","old",..: 1 3 2
 $ test : logi  TRUE FALSE TRUE

score <- c(5.0, 3.1, 2.4)
age <- c("child","young","old")
test <- c(TRUE, FALSE, TRUE)
d <- data.frame(score, age, test)

class(d)

 [1] "data.frame"

¹ The Factor class type was created here automatically for the 3 age categories.

Let's create and manipulate data objects in R

R For SAS Users