14 Feb R Matrices
A matrix is an arrangement of data in two-dimensional form. It has rows and columns. In this lesson, we will learn how to create a Matrix and work on some operations on R Matrices:
- Representation of a Matrix
- Create a Matrix
- Iterate a Matrix
- Get the Matrix length
- Access Matrix Items
- Find the number of rows and columns in a Matrix
Representation of a Matrix
To begin with, in the below figure, we have shown the representation of a matrix in the form of rows and columns. A row has a horizontal form whereas columns have a vertical form. It is a 3×3 matrix i.e. 3 rows and 3 columns:
Create a Matrix
To create a matrix in the R programming language, use the matrix() method. Using the nrow and ncol parameters, you need to set the number of rows and columns. In the below example, we have created a matrix. The c() is used to merge and concatenate the elements.
Let us see an example to create a matrix in the R programming language:
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# Create a matrix with 3 rows and 3 columns i.e. 9 elements # The nrow parameter sets the rows # The ncol parameter sets the columns myMatrix <- matrix(c(10, 15, 20, 25, 30, 35, 40, 45, 50), nrow = 3, ncol = 3) # Display myMatrix |
Output
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[,1] [,2] [,3] [1,] 10 25 40 [2,] 15 30 45 [3,] 20 35 50 |
Iterate a Matrix
To iterate a matrix in the R programming language, use the for loop. Let us see an example:
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# Create a matrix with 3 rows and 3 columns i.e. 9 elements # The nrow parameter sets the rows # The ncol parameter sets the columns myMatrix <- matrix(c(10, 15, 20, 25, 30, 35, 40, 45, 50), nrow = 3, ncol = 3) # Display the matrix myMatrix # Iterate and loop through for (rows in 1:nrow(myMatrix)) { for (columns in 1:ncol(myMatrix)) { # Iterate and display the matrix print(myMatrix[rows, columns]) } } |
Output
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[,1] [,2] [,3] [1,] 10 25 40 [2,] 15 30 45 [3,] 20 35 50 [1] 10 [1] 25 [1] 40 [1] 15 [1] 30 [1] 45 [1] 20 [1] 35 [1] 50 |
Matrix Length
The length() function is used to in the R programming language to get the matrix length. Let us see an example:
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# Create a matrix with 3 rows and 3 columns i.e. 9 elements # The nrow parameter sets the rows # The ncol parameter sets the columns myMatrix <- matrix(c(10, 15, 20, 25, 30, 35, 40, 45, 50), nrow = 3, ncol = 3) # Display the matrix myMatrix # Iterate and loop through length(myMatrix) |
Output
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[,1] [,2] [,3] [1,] 10 25 40 [2,] 15 30 45 [3,] 20 35 50 [1] 9 |
Access Matrix Items
Use the [ ] brackets in R to access the list items i.e. elements of a List. Two values need to be set as a parameter. The 1st is the row position and the 2nd position is a column. Just set the position numbers of the rows and columns for the element you want to fetch as in the below figure:
Let us see an example to access items from a matrix. We have access to all the items of a matrix to make the concept clear:
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# Create a matrix with 3 rows and 3 columns i.e. 9 elements # The nrow parameter sets the rows # The ncol parameter sets the columns myMatrix <- matrix(c(10, 15, 20, 25, 30, 35, 40, 45, 50), nrow = 3, ncol = 3) # Display the matrix myMatrix # Access items from a matrix myMatrix[1, 1] # 1st row 1st column myMatrix[1, 2] # 1st row 2nd column myMatrix[1, 3] # 1st row 3rd column myMatrix[2, 1] # 2nd row 1st column myMatrix[2, 2] # 2nd row 2nd column myMatrix[2, 3] # 2nd row 3rd column myMatrix[3, 1] # 3rd row 1st column myMatrix[3, 2] # 3rd row 2nd column myMatrix[3, 3] # 3rd row 3rd column |
Output
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[,1] [,2] [,3] [1,] 10 25 40 [2,] 15 30 45 [3,] 20 35 50 [1] 10 [1] 25 [1] 40 [1] 15 [1] 30 [1] 45 [1] 20 [1] 35 [1] 50 |
Find the number of rows and columns in a Matrix
The dim() function is used in the R programming language to find the number of rows and columns in a matrix. In the below example, we have a 3×3 matrix i.e. a matrix with 3 rows and 3 columns.
Let us see the example to find the count of rows and columns in an R matrix:
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# Create a matrix with 3 rows and 3 columns i.e. 9 elements # The nrow parameter sets the rows # The ncol parameter sets the columns myMatrix <- matrix(c(10, 15, 20, 25, 30, 35, 40, 45, 50), nrow = 3, ncol = 3) # Display the matrix myMatrix # Find the number of rows and columns in a Matrix dim(myMatrix) |
Output
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[,1] [,2] [,3] [1,] 10 25 40 [2,] 15 30 45 [3,] 20 35 50 [1] 3 3 |
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