Matrix creation in R Programming - Cheat Sheet & Quick Revision

Recall & Review

beginner

What function is used to create a matrix in R?

The matrix() function is used to create a matrix in R.

beginner

How do you specify the number of rows and columns when creating a matrix?

Use the arguments nrow for number of rows and ncol for number of columns inside the matrix() function.

intermediate

What does the argument byrow = TRUE do in matrix()?

It fills the matrix by rows instead of the default column-wise filling.

beginner

How can you create a 3x3 matrix with numbers 1 to 9 filled by rows?

Use matrix(1:9, nrow = 3, ncol = 3, byrow = TRUE).

intermediate

What happens if you provide fewer elements than needed for the matrix?

R recycles the elements to fill the matrix completely.

Which function creates a matrix in R?

A data.frame()

B matrix()

C array()

D list()

The matrix() function is specifically designed to create matrices.

What does byrow = TRUE do in matrix()?

A Fills matrix by rows

B Fills matrix by columns

C Creates a row vector

D Creates a column vector

Setting byrow = TRUE fills the matrix row-wise instead of the default column-wise.

How do you specify a matrix with 4 rows and 2 columns?

A matrix(data, rows=2, cols=4)

B matrix(data, nrow=2, ncol=4)

C matrix(data, rows=4, cols=2)

D matrix(data, nrow=4, ncol=2)

Use nrow and ncol to set rows and columns respectively.

What happens if you give fewer elements than needed in matrix()?

A R recycles elements to fill matrix

B R throws an error

C Matrix is partially filled with NA

D Matrix is created empty

R repeats the given elements to fill the entire matrix.

Which of these creates a 2x3 matrix filled by columns?

A matrix(1:6, nrow=3, ncol=2)

B matrix(1:6, nrow=2, ncol=3, byrow=TRUE)

C matrix(1:6, nrow=2, ncol=3)

D matrix(1:6, nrow=3, ncol=2, byrow=TRUE)

By default, matrix() fills by columns, so this creates a 2x3 matrix filled column-wise.

Explain how to create a matrix in R with 3 rows and 4 columns filled by rows.

Think about the function and its arguments for size and filling order.

What happens if the data vector is shorter than the matrix size when creating a matrix in R?

Consider how R handles insufficient data length.