Get element at the specific position from matrix in R

At any point in time, a matrix may be required to be traversed for an element at a specific position. In this article, we are going to access the elements from a matrix in R Programming Language using integer vector, logical vector as the index.

Method 1: Accessing elements using integer vector

Integer vector is a vector, that includes all elements of integer type.

Syntax:

matrix_name[row_vector_with_values,column_vector_with_values,]

Example:

select rows 1 & 3 and columns 1 & 3 of matrix a.

print(a )

Program:

R

# create a vector named data with 9 elements
data=c(1,2,3,4,5,6,7,8,9)

# pass this vector to matrix input
a=matrix(data, nrow = 3, ncol = 3)
print(a)

# select rows 1 & 3 and columns 1 & 3
print(a[c(1,3),c(1,3)] )

# select rows 1 & 2 and columns 1 & 2
print(a[c(1,2),c(1,2)] )

# select rows 2 & 1 and columns 2 & 2
print(a[c(2,1),c(2,2)] )

Output:

Method 2: Accessing matrix elements using logic vector

Logical vector includes a vector comprising boolean values i.e. TRUE or FALSE.

Syntax :

matrix_name[logical_vector]

If TRUE at that position, matrix element is accessed 

If FALSE at that position, matrix element is not accessed.

Example:

data=c(TRUE,TRUE,FALSE)

Program 1:

R

# create a vector named data with 9 elements
data=c(1,2,3,4,5,6,7,8,9)

# pass this vector to matrix input
a=matrix(data, nrow = 3, ncol = 3)
print(a)

a[c(TRUE, FALSE,TRUE, FALSE,TRUE, FALSE,TRUE, FALSE,TRUE)]
# accessing elements

Output:

Program 2:

R

# create a vector named data with 9 elements
data=c(1,2,3,4,5,6,7,8,9)

# pass this vector to matrix input
a=matrix(data, nrow = 3, ncol = 3)
print(a)

print(a[c(TRUE)])
# accessing elements by placing all TRUE

print(a[c(FALSE)])
# accessing elements by placing all FALSE

Output: