The **matrix()** function can be used to create a matrix in R:

(1) Create a **numeric matrix** with 3 rows and 2 columns – filled by **columns** (default):

my_matrix <- matrix(data = c(12, 15, 18, 23, 25, 27), nrow = 3, ncol = 2) print(my_matrix)

The result:

```
[,1] [,2]
[1,] 12 23
[2,] 15 25
[3,] 18 27
```

(2) Create a **numeric matrix** with 3 rows and 2 columns – filled by **rows** (‘TRUE’):

my_matrix <- matrix(data = c(12, 15, 18, 23, 25, 27), nrow = 3, ncol = 2, byrow = TRUE) print(my_matrix)

The result:

```
[,1] [,2]
[1,] 12 15
[2,] 18 23
[3,] 25 27
```

(3) Create a **categorial matrix** with 3 rows and 2 columns – filled by **columns** (default):

my_matrix <- matrix(data = c("A", "B", "C", "D", "A", "C"), nrow = 3, ncol = 2) print(my_matrix)

The result:

```
[,1] [,2]
[1,] "A" "D"
[2,] "B" "A"
[3,] "C" "C"
```

(4) Create a **categorial matrix** with 3 rows and 2 columns – filled by **rows** (‘TRUE’):

my_matrix <- matrix(data = c("A", "B", "C", "D", "A", "C"), nrow = 3, ncol = 2, byrow = TRUE) print(my_matrix)

The result:

```
[,1] [,2]
[1,] "A" "B"
[2,] "C" "D"
[3,] "A" "C"
```