matrix()

matrix(data, nrow, ncol, byrow, dimnames)

Matrices are two-dimensional data structures in R that hold elements of the same atomic type. They are fundamental to statistical computing and linear algebra.

Syntax

matrix(data, nrow, ncol, byrow, dimnames)

Parameters

Parameter	Type	Default	Description
data	any	—	An atomic vector (or scalar) to fill the matrix
nrow	integer	—	Number of rows
ncol	integer	—	Number of columns
byrow	logical	FALSE	Fill matrix by rows if TRUE, by columns if FALSE
dimnames	list	NULL	Optional row and column names

Examples

Basic matrix creation

# Create a 3x2 matrix filled column-wise (default)
mat <- matrix(1:6, nrow = 3, ncol = 2)
mat
#      [,1] [,2]
# [1,]    1    4
# [2,]    2    5
# [3,]    3    6

# Fill by rows instead
mat_by_row <- matrix(1:6, nrow = 3, ncol = 2, byrow = TRUE)
mat_by_row
#      [,1] [,2]
# [1,]    1    2
# [2,]    3    4
# [3,]    5    6

Named rows and columns

# Add row and column names
mat <- matrix(1:6, nrow = 3, ncol = 2,
              dimnames = list(c("r1", "r2", "r3"),
                              c("c1", "c2")))
mat
#    c1 c2
# r1  1  4
# r2  2  5
# r3  3  6

Matrix operations

# Matrix multiplication
A <- matrix(1:4, nrow = 2)
B <- matrix(5:8, nrow = 2)
A %*% B
#      [,1] [,2]
# [1,]   23   34
# [2,]   34   50

# Transpose
t(A)
#      [,1] [,2]
# [1,]    1    3
# [2,]    2    4

# Row and column sums
rowSums(A)
# [1] 3 7
colSums(A)
# [1] 4 6

Common Patterns

Matrix indexing

mat <- matrix(1:9, nrow = 3)

# Access element
mat[2, 3]
# [1] 8

# Access row
mat[1, ]
# [1] 1 4 7

# Access column
mat[, 2]
# [1] 4 5 6

Binding vectors

# Combine vectors as rows
rbind(1:3, 4:6)
#      [,1] [,2] [,3]
# [1,]    1    2    3
# [2,]    4    5    6

# Combine vectors as columns
cbind(1:3, 4:6)
#      [,1] [,2]
# [1,]    1    4
# [2,]    2    5
# [3,]    3    6

Diagonal matrices

# Identity matrix
diag(3)
#      [,1] [,2] [,3]
# [1,]    1    0    0
# [2,]    0    1    0
# [3,]    0    0    1

# Custom diagonal
diag(c(1, 2, 3))
#      [,1] [,2] [,3]
# [1,]    1    0    0
# [2,]    0    2    0
# [3,]    0    0    3

See Also

• data.frame()
• colnames()
• rownames()