Multiply Matrix by Vector in R

A matrix is a 2-dimensional structure whereas a vector is a one-dimensional structure. In this article, we are going to multiply the given matrix by the given vector using R Programming Language. Multiplication between the two occurs when vector elements are multiplied with matrix elements column-wise.

Approach:

• Create a matrix
• Create a vector
• Multiply them
• Display result.

Method 1: Naive method

Once the structures are ready we directly multiply them using the multiplication operator(*).

Example:

R

# create a vector for matrix elements
vector1=c(1,2,3,4,5,6,7,8,9,10,11,12)

# Create A matrix with 2 rows and 6 columns
matrix1 <- matrix(vector1, nrow=2,ncol=6)

# multiplication vector
mul_vec=c(1,2,3,4)

# print multiplication result
print(matrix1*mul_vec)

Output:

Example 2:

R

# create a vector for matrix elements
vector1=c(1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16)

# Create A matrix with 4 rows and 4 columns
matrix1 <- matrix(vector1, nrow=4,ncol=4)
print(matrix1)

mul_vec=c(1,2,3,4)

print("Result")
print(matrix1*mul_vec)

Output:

Example 3:

This code has both matrix and vector has equal size

R

# create a vector for matrix elements
vector1=c(1,2,3,4)

# Create A matrix with 2 rows and 2 columns
matrix1 <- matrix(vector1,nrow=2,ncol=2)
print(matrix1)

mul_vec=c(1,2,3,4)

print("Result")
print(matrix1*mul_vec)

Output:

Method 2: Using sweep()

we can use sweep() method to multiply vectors to a matrix. sweep() function is used to apply the operation “+ or – or ‘*’ or ‘/’ ” to the row or column in the given matrix.

Syntax:

sweep(data, MARGIN,  FUN)

Parameter:

• data=input matrix
• MARGIN: MARGIN = 2 means row; MARGIN = 1 means column.
• FUN: The operation that has to be done (e.g. + or – or * or /)

Here, we are performing “*” operation

Example:

R

# create matrix with 15 elements
matrix1 <- matrix(c(1,2,3,4,5,6,7,8,9,10,11,12,13,14,15),
                  nrow=3,byrow=TRUE)
print(matrix1)
print("---------------")

# create a vector
vector1 <- c(1,2,3,4,5)

# apply sweep operation that multiplies row
# wise(margin=2)
print(sweep(matrix1, MARGIN=2,vector1, `*`))
print("---------------")

# create elements with vector 2
vector2 <- c(1,2,3)

# apply sweep operation that multiplies column
# wise with vector 2(margin=1)
print(sweep(matrix1, MARGIN=1,vector2, `*`))

Output:

Example 2:

R

# create matrix with 8 elements
matrix1 <- matrix(c(1,2,3,4,5,6,7,8),
                  nrow=2,byrow=TRUE)
print(matrix1)
print("---------------")

# create a vector
vector1 <- c(1,2,3,4)

# apply sweep operation that multiplies
# row wise(margin=2)
print(sweep(matrix1, MARGIN=2,vector1, `*`))
print("---------------")

# create elements with vector 2
vector2 <- c(1,2)

# apply sweep operation that multiplies column
# wise with vector 2(margin=1)
print(sweep(matrix1, MARGIN=1,vector2, `*`))

Output: