The Class of an Object In R Language

Introduction to Class of an Object in R

In R language, all objects have a class, which can be reported using the class() function. For simple vectors, this is just the mode, such as numeric, character, list, or logical. The other possible modes are array, matrix, factor, and data frame.

A special attribute known as the class of the object is used to allow for an object-oriented style of programming in R language. For example, an object having class as “data.frame” will be printed in a certain way, the plot() function will display it graphically in a certain way, and other generic functions such as summary() will react to it as an argument in a way sensitive to its class.

How to Determine the Class of an Object in R

The class() function is used to determine the class of an object. For example,

class(mtcars)
x <- c(1, 2, 3)
class(x)

y <- c("a", "b", "c")
class(y)

z <- c(TRUE, FALSE)
class(z)

Common Object Classes in R

Here are some of the most common object classes in R:

1. Integer: Represents integer values.
2. Numeric: Represents numerical data.
3. Character: Represents text strings.
4. Factor: Represents categorical data.
5. Logical: Represents logical values (TRUE or FALSE).
6. Date: Represents dates.
7. List: Represents a collection of objects of different types.
8. Matrix: Represents a two-dimensional array of numbers.
9. Data Frame: Represents a tabular data structure with rows and columns.
10. POSIXct: Represents date and time.

It is important to note that one can define one’s classes using S3 or S4 object-oriented systems. This allows the user to define specific methods and behavior for different objects.

Why Classes Matter in R Language

The class of an object determines how R behaves when a user applies functions to it. In simple words, a class defines the object’s type and determines the operations that can be performed on it. For instance:

• Arithmetic operations: These are typically performed on numeric objects.
• String manipulation: These are performed on character objects.
• Statistical analysis: These are often performed on numeric or factor objects.

The importance of classes can be described as:

• Method Dispatch: The class of an object in R language determines which function to call when you apply a generic function to it. For example, the summary() function behaves differently for numeric vectors, data frames, and linear models.
• Object-Oriented Programming: R supports object-oriented programming, and classes are fundamental to this paradigm. One can create custom classes to represent complex data structures and define methods to operate on these objects.
• Data Manipulation: Understanding the class of an object helps one to choose the appropriate functions for data manipulation. For instance, one might use different functions for subsetting, sorting, and summarizing numeric vectors, character vectors, and data frames.

Remove the Class of an Object in R

To remove temporarily the effect of a class from an object, one can use the unclass() function. For example, if mtcars has the class “data.frame” then typing the just mtcars on the command prompt will print it in data frame form, which is rather like a matrix.

mtcars

Whereas, typing unclass(mtcars) will print/display it as an ordinary list.

unclass(mtcars)

## Output
$mpg
 [1] 21.0 21.0 22.8 21.4 18.7 18.1 14.3 24.4 22.8 19.2 17.8 16.4 17.3 15.2 10.4 10.4 14.7 32.4 30.4 33.9 21.5 15.5 15.2 13.3 19.2 27.3 26.0 30.4 15.8 19.7 15.0 21.4

$cyl
 [1] 6 6 4 6 8 6 8 4 4 6 6 8 8 8 8 8 8 4 4 4 4 8 8 8 8 4 4 4 8 6 8 4

$disp
 [1] 160.0 160.0 108.0 258.0 360.0 225.0 360.0 146.7 140.8 167.6 167.6 275.8 275.8 275.8 472.0 460.0 440.0  78.7  75.7  71.1 120.1 318.0 304.0 350.0 400.0  79.0 120.3  95.1 351.0 145.0 301.0 121.0

$hp
 [1] 110 110  93 110 175 105 245  62  95 123 123 180 180 180 205 215 230  66  52  65  97 150 150 245 175  66  91 113 264 175 335 109

$drat
 [1] 3.90 3.90 3.85 3.08 3.15 2.76 3.21 3.69 3.92 3.92 3.92 3.07 3.07 3.07 2.93 3.00 3.23 4.08 4.93 4.22 3.70 2.76 3.15 3.73 3.08 4.08 4.43 3.77 4.22 3.62 3.54 4.11

$wt
 [1] 2.620 2.875 2.320 3.215 3.440 3.460 3.570 3.190 3.150 3.440 3.440 4.070 3.730 3.780 5.250 5.424 5.345 2.200 1.615 1.835 2.465 3.520 3.435 3.840 3.845 1.935 2.140 1.513 3.170 2.770 3.570 2.780

$qsec
 [1] 16.46 17.02 18.61 19.44 17.02 20.22 15.84 20.00 22.90 18.30 18.90 17.40 17.60 18.00 17.98 17.82 17.42 19.47 18.52 19.90 20.01 16.87 17.30 15.41 17.05 18.90 16.70 16.90 14.50 15.50 14.60 18.60

$vs
 [1] 0 0 1 1 0 1 0 1 1 1 1 0 0 0 0 0 0 1 1 1 1 0 0 0 0 1 0 1 0 0 0 1

$am
 [1] 1 1 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 1 1 0 0 0 0 0 1 1 1 1 1 1 1

$gear
 [1] 4 4 4 3 3 3 3 4 4 4 4 3 3 3 3 3 3 4 4 4 3 3 3 3 3 4 5 5 5 5 5 4

$carb
 [1] 4 4 1 1 2 1 4 2 2 4 4 3 3 3 4 4 4 1 2 1 1 2 2 4 2 1 2 2 4 6 8 2

attr(,"row.names")
 [1] "Mazda RX4"       "Mazda RX4 Wag"    "Datsun 710"       "Hornet 4 Drive"   "Hornet Sportabout"
 [6] "Valiant"         "Duster 360"       "Merc 240D"        "Merc 230"         "Merc 280"
[11] "Merc 280C"       "Merc 450SE"       "Merc 450SL"       "Merc 450SLC"      "Cadillac Fleetwood" 
[16] "Lincoln Continental" "Chrysler Imperial"   "Fiat 128"      "Honda Civic"     "Toyota Corolla" 
[21] "Toyota Corona"    "Dodge Challenger"  "AMC Javelin"     "Camaro Z28"      "Pontiac Firebird"   
[26] "Fiat X1-9"       "Porsche 914-2"     "Lotus Europa"     "Ford Pantera L"  "Ferrari Dino"       
[31] "Maserati Bora"   "Volvo 142E"

Changing the Class of an Object in R

While it’s generally not recommended to manually change an object’s class, there are functions like as.numeric(), as.character(), as.factor(), etc., that can coerce objects into different classes. However, be cautious, as inappropriate coercion can lead to unexpected results.

Understanding object classes is fundamental to effective R programming. By recognizing the class of an object, you can choose the appropriate functions and operations to work with it. By understanding the class of an object, you can effectively work with R’s diverse data structures and leverage its powerful data analysis capabilities.

FAQs about Class of an Object

1. What is the concept of class in R language?
2. How can one check the class of an object?
3. For different data types (modes) what are the common classes used in R?
4. How can one change the class of an object?
5. Give examples to determine the class of different objects.

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