is.matrix() Function: Check If an Object is a Matrix in R

The is.matrix() is a built-in R function that checks whether an input object is a matrix. It returns TRUE if the object is a matrix and FALSE otherwise.

To prevent unexpected errors, you need to check if the input object is a matrix, and that’s where we need this function. It makes our code more predictable and reliable.

Syntax

is.matrix(obj)

Parameters

Visual representation

Checking matrix

Let’s define a 3X3 matrix.

mat <- matrix(1:9, nrow = 3, ncol = 3)

mat # 3x3 matrix

is.matrix(mat) # TRUE

Output

If you pass a vector as an argument, it will return FALSE.

vec <- c(1, 2, 3)

is.matrix(vec) # FALSE

Usage with a conditional statement

Conditional statements like “if” can be used with is.matrix() function to check if it is a matrix, and if yes, then we can use the “apply()” function to it.

mat <- matrix(1:9, nrow = 3, ncol = 3)

col_means <- function(mtrx) {
  if (!is.matrix(mtrx)) {
    stop("Input must be a matrix")
  }
  apply(mtrx, 2, mean)
}

col_means(mat)

Output

[1] 2  5  8

Since the input object is a matrix, we used the apply() function to get the mean of each column.

If the input object is not a matrix, it stops and prints an error message.

Checking NA values

NA represents missing values, and missing values can be anything. If a matrix contains NA values, is.matrix() function returns TRUE.

mat_with_na <- matrix(c(19, 21, NA, 10), nrow = 2)

is.matrix(mat_with_na) # TRUE

If you pass the NA value to this function, it returns FALSE.

na_val <- NA

is.matrix(na_val) # FALSE

Checking NaN (Not a Number)

NaN represents undefined numerical results. (e.g., 0/0, Inf – Inf). If a matrix contains NaN, it still returns TRUE.

mat_with_nan <- matrix(c(19, 21, NaN, 10), nrow = 2)

is.matrix(mat_with_nan) # TRUE

If you pass the NaN value to this function, it returns FALSE.

nan_val <- NaN

is.matrix(nan_val) # FALSE

That’s all!