Notice: This page requires JavaScript to function properly.
Please enable JavaScript in your browser settings or update your browser.Matrix Indexation | Matrices
R Introduction: Part II
course content

Course Content

R Introduction: Part II

R Introduction: Part II

1. Matrices
What is a Matrix?matrix() FunctionTransposingMatrix IndexationNamingsOperation with MatricesSales and Revenue
2. Data Frames
What is a Data Frame?data.frame() FunctionColumns AccessorsLogical IndexingManipulating ColumnsManipulating RowsData Extraction
3. Lists
What is a List?NamingsExtracting List ElementsModifying

bookMatrix Indexation

Good. Now you know how to create a matrix in several ways. Let's work with already created objects. First, we need to learn how to access certain matrix elements.

Back to the Vectors section, you should remember that indexation in R starts with 1. Since the matrix is a two-dimensional structure, we need to refer to two positions: among rows and columns. Like in vectors, you need to use square brackets and put two integers (the first is the row number, the second is the column number) divided by a comma. For example, let's extract element 5 (row 2, column 2) and 3 (row 1, column 3) from the matrix below.


              
123456789

            
# Vector of integers
num <- 1:9
# Matrix
m <- matrix(num, nrow = 3, ncol = 3, byrow = T)

# Element `5`
m[2, 2]
# Element `3`
m[1, 3]
copy

Also you can extract multiple rows and/or columns at once. Pass vector of indices instead of a single index. For example, we can extract the 2nd and 3rd columns for the 3rd row.


              
1234

            
num <- 1:9
m <- matrix(num, nrow = 3, ncol = 3, byrow = T)
# 2nd and 3rd columns for 3rd row
m[3, c(2,3)]
copy

If you want to extract an entire row/column, do not set an index for the remaining part. For example, let's pull the first row and the third column.


              
123456

            
num <- 1:9
m <- matrix(num, nrow = 3, ncol = 3, byrow = T)
# The first row
m[1,]
# The third column
m[,3]
copy

Task

Given matrix named m.

Your tasks are:

  1. Extract the element 12.
  2. Extract the elements 4 6.
  3. Extract the third column.

Switch to desktopSwitch to desktop for real-world practiceContinue from where you are using one of the options below
Everything was clear?

How can we improve it?

Thanks for your feedback!

Section 1. Chapter 4
toggle bottom row

bookMatrix Indexation

Good. Now you know how to create a matrix in several ways. Let's work with already created objects. First, we need to learn how to access certain matrix elements.

Back to the Vectors section, you should remember that indexation in R starts with 1. Since the matrix is a two-dimensional structure, we need to refer to two positions: among rows and columns. Like in vectors, you need to use square brackets and put two integers (the first is the row number, the second is the column number) divided by a comma. For example, let's extract element 5 (row 2, column 2) and 3 (row 1, column 3) from the matrix below.


              
123456789

            
# Vector of integers
num <- 1:9
# Matrix
m <- matrix(num, nrow = 3, ncol = 3, byrow = T)

# Element `5`
m[2, 2]
# Element `3`
m[1, 3]
copy

Also you can extract multiple rows and/or columns at once. Pass vector of indices instead of a single index. For example, we can extract the 2nd and 3rd columns for the 3rd row.


              
1234

            
num <- 1:9
m <- matrix(num, nrow = 3, ncol = 3, byrow = T)
# 2nd and 3rd columns for 3rd row
m[3, c(2,3)]
copy

If you want to extract an entire row/column, do not set an index for the remaining part. For example, let's pull the first row and the third column.


              
123456

            
num <- 1:9
m <- matrix(num, nrow = 3, ncol = 3, byrow = T)
# The first row
m[1,]
# The third column
m[,3]
copy

Task

Given matrix named m.

Your tasks are:

  1. Extract the element 12.
  2. Extract the elements 4 6.
  3. Extract the third column.

Switch to desktopSwitch to desktop for real-world practiceContinue from where you are using one of the options below
Everything was clear?

How can we improve it?

Thanks for your feedback!

Section 1. Chapter 4
toggle bottom row

bookMatrix Indexation

Good. Now you know how to create a matrix in several ways. Let's work with already created objects. First, we need to learn how to access certain matrix elements.

Back to the Vectors section, you should remember that indexation in R starts with 1. Since the matrix is a two-dimensional structure, we need to refer to two positions: among rows and columns. Like in vectors, you need to use square brackets and put two integers (the first is the row number, the second is the column number) divided by a comma. For example, let's extract element 5 (row 2, column 2) and 3 (row 1, column 3) from the matrix below.


              
123456789

            
# Vector of integers
num <- 1:9
# Matrix
m <- matrix(num, nrow = 3, ncol = 3, byrow = T)

# Element `5`
m[2, 2]
# Element `3`
m[1, 3]
copy

Also you can extract multiple rows and/or columns at once. Pass vector of indices instead of a single index. For example, we can extract the 2nd and 3rd columns for the 3rd row.


              
1234

            
num <- 1:9
m <- matrix(num, nrow = 3, ncol = 3, byrow = T)
# 2nd and 3rd columns for 3rd row
m[3, c(2,3)]
copy

If you want to extract an entire row/column, do not set an index for the remaining part. For example, let's pull the first row and the third column.


              
123456

            
num <- 1:9
m <- matrix(num, nrow = 3, ncol = 3, byrow = T)
# The first row
m[1,]
# The third column
m[,3]
copy

Task

Given matrix named m.

Your tasks are:

  1. Extract the element 12.
  2. Extract the elements 4 6.
  3. Extract the third column.

Switch to desktopSwitch to desktop for real-world practiceContinue from where you are using one of the options below
Everything was clear?

How can we improve it?

Thanks for your feedback!

Good. Now you know how to create a matrix in several ways. Let's work with already created objects. First, we need to learn how to access certain matrix elements.

Back to the Vectors section, you should remember that indexation in R starts with 1. Since the matrix is a two-dimensional structure, we need to refer to two positions: among rows and columns. Like in vectors, you need to use square brackets and put two integers (the first is the row number, the second is the column number) divided by a comma. For example, let's extract element 5 (row 2, column 2) and 3 (row 1, column 3) from the matrix below.


              
123456789

            
# Vector of integers
num <- 1:9
# Matrix
m <- matrix(num, nrow = 3, ncol = 3, byrow = T)

# Element `5`
m[2, 2]
# Element `3`
m[1, 3]
copy

Also you can extract multiple rows and/or columns at once. Pass vector of indices instead of a single index. For example, we can extract the 2nd and 3rd columns for the 3rd row.


              
1234

            
num <- 1:9
m <- matrix(num, nrow = 3, ncol = 3, byrow = T)
# 2nd and 3rd columns for 3rd row
m[3, c(2,3)]
copy

If you want to extract an entire row/column, do not set an index for the remaining part. For example, let's pull the first row and the third column.


              
123456

            
num <- 1:9
m <- matrix(num, nrow = 3, ncol = 3, byrow = T)
# The first row
m[1,]
# The third column
m[,3]
copy

Task

Given matrix named m.

Your tasks are:

  1. Extract the element 12.
  2. Extract the elements 4 6.
  3. Extract the third column.

Switch to desktopSwitch to desktop for real-world practiceContinue from where you are using one of the options below
Section 1. Chapter 4
Switch to desktopSwitch to desktop for real-world practiceContinue from where you are using one of the options below
some-alt