# Matrix in R Language (2015): Key Secrets

The matrix is an important data type in R language similar to the data frame. It has two dimensions as the arrangement of elements is in rows and columns.

### Matrix In R Language

Question: What is a matrix in R Language?
Answer: In R language matrices are two-dimensional arrays of elements all of which are of the same type, for example, numbers, character strings, or logical values.

Matrices may be constructed using the built-in function “matrix”, which reshapes its first argument into a matrix having a specified number of rows as the second argument and a number of columns as the third matrix.

### Creating a Matrix in R Language

Question: Give an example of how the matrix is constructed in R language.
Answer: A 3 by 3 matrix (3 rows and 3 columns) matrix may be constructed such as:

matrix(1:9, 3, 3)
matrix(c(1,2,3,4,5,6,7,8,9), 3, 3)
matrix(runif(9), 3,3)

First, two commands construct a matrix of 9 elements having 3 rows and 3 columns consisting of numbers from 1 up to 9. The third command makes a matrix of 3 rows and 3 columns with random numbers from a uniform distribution.

Question: How the matrix elements are filled?
Answer: A matrix is filled by columns, unless the optional argument byrow is set to TRUE as an argument in matrix command, for example

matrix(1:9, 3, 3, byrow = TRUE)

Question: Can the matrix be stored in R?
Answer: Any matrix can be stored in R such as

m <- matrix(1:9, 3, 3)
mymatrix <- matrix( rnorm(16), nrow=4 )

Matrices are stored in “m” and “mymatrix” objects. The second command constructs a matrix having 16 elements with 4 rows from a normal distribution having mean 0 and variance 1.

### Attributes of Matrix Object in R

Question: What is the use of the dim command in R?
Answer: The dim (dimension) is an attribute of the matrix in R language, which tells the number of rows and the number of columns of a matrix, for example,

dim(mymatrix)

This will result in output showing 4  4, meaning 4 rows and 4 column matrix.

Question: Can we name rows of a matrix in R Language?
Answer: Yes in R language we can name rows of a matrix according to one’s requirements, such as

rownames(mymatrix) &lt;- c("x1", "x2", "x3", "x4")
mymatrix

Question: Can column names be changed or updated in R?
Answer: The procedure is the same as changing the column name. For this purpose colnames command is used, for example

colnames(mymatrix)&lt;-c("A", "B", "C", "D")
mymatrix

Question: What is the purpose of the attributes command for the matrix in R Language?
Answer: The attributes function can be used to get information about the dimension of the matrix and dimnames (dimension names). For example;

attributes(mymatrix)

In summary, the primary function for creating a matrix in R language is matrix(). It takes a few arguments:

• data: This is a vector containing the elements for the matrix.
• nrow: The number of rows in the matrix.
• ncol: The number of columns in the matrix.

### FAQs about Matrices in R

1. How to create a matrix in R?
2. How elements are filled in R?
3. How to convert a data object to a matrix object in R?
4. How different attributes of a matrix in R can be checked?
5. How matrices can be stored in a variable?
6. How one can name the rows and columns of a matrix in R?
7. What is the difference between dim and dimnames commands?
8. How one can create a matrix of order 3 by 3 (3 rows and 3 columns) with elements from a probability Distribution.
9. What is the primary function of matrix() function in R Language.

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