Matrix dimensions in R Programming - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

What is the output of this R code for matrix dimensions?

Consider the following R code that creates a matrix and then checks its dimensions. What will be printed?

R Programming

m <- matrix(1:12, nrow=3, ncol=4)
dim(m)

A [1] 12

B [1] 3 4

C [1] 4 3

D NULL

💡 Hint

The dim() function returns the number of rows and columns in that order.

The matrix m has 3 rows and 4 columns, so dim(m) returns a vector with 3 and 4.

❓ Predict Output

intermediate

What does this code print for matrix dimensions after transpose?

Given the matrix m and its transpose t(m), what will dim(t(m)) return?

R Programming

m <- matrix(1:6, nrow=2, ncol=3)
dim(t(m))

A [1] 3 2

B [1] 2 3

C [1] 6

D NULL

💡 Hint

Transpose swaps rows and columns.

Original matrix has 2 rows and 3 columns, transpose swaps them to 3 rows and 2 columns.

❓ Predict Output

advanced

What is the output of dim() on a vector converted to matrix?

What will be the output of dim() when applied to a vector converted to a matrix with one column?

R Programming

v <- 1:5
m <- matrix(v, ncol=1)
dim(m)

A [1] 1 5

B [1] 5

C [1] 5 1

D NULL

💡 Hint

Matrix with ncol=1 means one column and rows equal to length of vector.

The matrix has 5 rows and 1 column, so dim returns c(5,1).

❓ Predict Output

advanced

What error or output occurs when dim() is applied to a list?

What happens when you run dim() on a list in R?

R Programming

lst <- list(a=1, b=2)
dim(lst)

A [1] 1 2

B Error in dim(lst) : 'dim' applied to non-array

C [1] 2

D NULL

💡 Hint

Lists do not have dimensions like matrices or arrays.

dim() returns NULL for lists because they do not have dimensions.

🧠 Conceptual

expert

How many elements are in a matrix with dim attribute c(4,5)?

If a matrix in R has dimensions 4 rows and 5 columns, how many elements does it contain?

A 20

B 5

C 10

D 9

💡 Hint

Multiply rows by columns to get total elements.

A matrix with 4 rows and 5 columns has 4*5 = 20 elements.