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

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Featured Image of is.matrix() Function

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

Name Value
obj It is an input variable that will be checked for a matrix.

Visual representation

Visual Representation of is.matrix() Function

Checking matrix

Let’s define a 3X3 matrix.

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

mat # 3x3 matrix

is.matrix(mat) # TRUE

Output

Output of is.matrix() Function

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!

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