Data Structure: Matrix

↪ Creating a matrix

A matrix is a two-dimensional table with rows and columns of data. Like vectors, R matrices can contain one type of data and are typically used for only storing numeric data.

Creating a matrix from two vectors using cbind() function.

      x = c(2,3,4,5)
      y = c(5,6,7,8)
      z = cbind(x,y)
      z

      ---Output---
      -    x y
      [1,] 2 5
      [2,] 3 6
      [3,] 4 7
      [4,] 5 8

Creating a matrix with an initial element, say initial element = 1, using the function matrix(initial element, row, column).

      z = matrix(1,2,4)
      z

      ---Output---
      -    [,1] [,2] [,3] [,4]
      [1,]    1    1    1    1
      [2,]    1    1    1    1

Creating a matrix from vector using function matrix(vector, row, column).

      z = matrix(x,2,2)
      z

      ---Output---
      -    [,1] [,2]
      [1,]    2    4
      [2,]    3    5

Creating a matrix by specifying a number of rows or columns with the vector.

      m <- matrix(c(10, 20, 30, 40), nrow = 2)
      m
      -    [,1] [,2]
      [1,]   10   30
      [2,]   20   40

      m <- matrix(c(10, 20, 30, 40), ncol = 2)
      m

R loads the data column by default. This method is called column-major order. This behavior can be overridden by byrow = TRUE while creating the matrix.

      m <- matrix(c(10, 20, 30, 40), ncol = 2, byrow=TRUE)
      m

      ---Output---
      -    [,1] [,2]
      [1,]   10   20
      [2,]   30   40

Data Structure: Matrix

↪ Accessing matrix

Accessing matrix row

      z[1,]

Accessing matrix column

      z[,2]

Accessing matrix element

      z[2,2]

Transpose of a matrix

      t(z)

Inverse of a matrix

      solve(z)