R Matrices

In mathematics, a matrix is a rectangular array of numbers, symbols, or expressions, arranged in rows and columns. You can create matrix in R using matrix() function.

> matrix1 <- matrix(nrow=2, ncol=4)
> matrix1
     [,1] [,2] [,3] [,4]
[1,]   NA   NA   NA   NA
[2,]   NA   NA   NA   NA
> 
> dim(matrix1)
[1] 2 4
> 
> attributes(matrix1)
$dim
[1] 2 4

matrix1 <- matrix(nrow=2, ncol=4)

Above statement creates a matrix with number of rows 2 and number of columns 4.

dim(matrix1)

dim function returns the dimensions of given matrix.

Matrices in R language are constructed in column-wise.

> matrix2 <- matrix(1:6, nrow=2, ncol=3)
> matrix2
     [,1] [,2] [,3]
[1,]    1    3    5
[2,]    2    4    6 

As you observe above snippet, elements

1,2 are stored in column1

3,4 are stored in column2

5,6 are stored in column3

Accessing elements of Matrix

You can access elements of matrix using “matrixName[row, column]”.

> matrix2[1,1]
[1] 1
> matrix2[1,2]
[1] 3
> matrix2[1,3]
[1] 5
> matrix2[2,1]
[1] 2
> matrix2[2,2]
[1] 4
> matrix2[2,3]
[1] 6

In the same you access elements, you can assign values to matrices.

> matrix2[1,1]<-100
> matrix2
     [,1] [,2] [,3]
[1,]  100    3    5
[2,]    2    4    6

Get the transpose of a matrix

You can get the transpose of a matrix by using t() function.

> matrix2
     [,1] [,2] [,3]
[1,]  100    3    5
[2,]    2    4    6
> 
> matrix3 = t(matrix2)
> 
> matrix3
     [,1] [,2]
[1,]  100    2
[2,]    3    4
[3,]    5    6

Deconstruct matrix

You can deconstruct matrix by using c() function.

> matrix3
     [,1] [,2]
[1,]  100    2
[2,]    3    4
[3,]    5    6
> 
> c(matrix3)
[1] 100   3   5   2   4   6

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