R object classes

R objects can be of several different “classes” A class essentially describes what kind of information is contained in the object

Numeric

Often an object contains “numeric” class data, like a number or vector of numbers We can test the class of an object using class:

class(12)

## [1] "numeric"

class(c(1, 1.5, 2))

## [1] "numeric"

While most numbers are of class “numeric”, a subset are “integer”:

class(1:5)

## [1] "integer"

We can coerce numeric class objects to an integer class:

as.integer(c(1, 1.5, 2))

## [1] 1 1 2

But note that this modifies the second item in the vector (1.5 becomes 1)

Character

Other common classes include “character” data We see character class data in country names or certain survey responses

class("United States")

## [1] "character"

If we try to coerce character to numeric, we get a warning and the result is a missing value:

as.numeric("United States")

## Warning: NAs introduced by coercion

## [1] NA

If we combine a numeric (or integer) and a character together in a vector, the result is character:

class(c(1, "test"))

## [1] "character"

You can see that the 1 is coerced to character:

c(1, "test")

## [1] "1"    "test"

We can also coerce a numeric vector to character simply by changing its class:

a <- 1:4
class(a)

## [1] "integer"

class(a) <- "character"
class(a)

## [1] "character"

a

## [1] "1" "2" "3" "4"

Factor

Another class is “factor” Factors are very important to R, especially in regression modelling Factors combine characteristics of numeric and character classes We can create a factor from numeric data using factor:

factor(1:3)

## [1] 1 2 3
## Levels: 1 2 3

We see that factor displays a special levels attribute Levels describe the unique values in the vector e.g., with the following factor, there are six values but only two levels:

factor(c(1, 2, 1, 2, 1, 2))

## [1] 1 2 1 2 1 2
## Levels: 1 2

To see just the levels, we can use the levels function:

levels(factor(1:3))

## [1] "1" "2" "3"

levels(factor(c(1, 2, 1, 2, 1, 2)))

## [1] "1" "2"

We can also build factors from character data:

factor(c("a", "b", "b", "c"))

## [1] a b b c
## Levels: a b c

We can look at factors in more detail in the factors.R script

Logical

Another common class is “logical” data This class involves TRUE | FALSE objects We can look at that class in detail in the logicals.R script