matrix row names in r code example

Example 1: how to create a matrix with row and column names in r

> x <- matrix(1:9, nrow = 3, dimnames = list(c("X","Y","Z"), c("A","B","C")))
> x
A B C
X 1 4 7
Y 2 5 8
Z 3 6 9
> colnames(x)
[1] "A" "B" "C"
> rownames(x)
[1] "X" "Y" "Z"
> # It is also possible to change names
> colnames(x) <- c("C1","C2","C3")
> rownames(x) <- c("R1","R2","R3")
> x
C1 C2 C3
R1  1  4  7
R2  2  5  8
R3  3  6  9

Example 2: get matrix row name r

> grades_matrix
             Math      Science          Art
Student_1      90           88           75
Student_2      78           81           95 
Student_3      84           85           83

> rownames(grade_matrix)[2]
[1] "Student_2"

> colnames(grade_matrix)[3]
[1] "Art"