How to Use the identical() Function in R

In data analysis and scientific computing, it’s quite common to compare objects for equality. R, being a language designed for statistical analysis, offers a function that aids in comparing objects for absolute equality: the identical() function. This function is powerful, as it tests if two objects are exactly equal, taking the type of data and attributes into account.

In this comprehensive guide, we will explore the identical() function in R, illustrating its syntax, basic usage, nuances, and applications across different scenarios.

Overview of identical()

The identical() function in R compares two R objects for absolute equality, meaning it tests whether the two objects are exactly the same in terms of their contents, their data type, and their attributes (if any). This function is more rigid than the == operator, which only compares the contents of two objects and can sometimes lead to unexpected results due to type coercion.

The basic syntax of the identical() function in R is as follows:

identical(object1, object2)

Here, object1 and object2 are the two R objects you want to compare.

Basic Usage of identical()

To understand how to use the identical() function, let’s start with a basic example. We’ll create two numeric vectors and use the identical() function to compare them:

# Define the vectors
vector1 <- c(1, 2, 3, 4, 5)
vector2 <- c(1, 2, 3, 4, 5)

# Use identical() to compare the vectors
is_identical <- identical(vector1, vector2)

# Print the result
print(is_identical)

When you run this code, the output will be TRUE, as vector1 and vector2 are identical in terms of their contents and data type.

Differences from the == Operator

As mentioned earlier, the identical() function differs from the == operator. The == operator only compares the contents of two objects and may sometimes lead to unexpected results due to type coercion.

Let’s illustrate this difference with an example. We’ll create two objects: a numeric vector and a character vector:

# Define the vectors
vector1 <- c(1, 2, 3)
vector2 <- c("1", "2", "3")

# Compare using ==
print(vector1 == vector2)

# Compare using identical()
print(identical(vector1, vector2))

When you run this code, the output will be:

[1] TRUE TRUE TRUE
[1] FALSE

As you can see, the == operator returns TRUE for each comparison, as it coerces the numeric values to character values before the comparison. On the other hand, the identical() function returns FALSE, as it takes into account the data type of the vectors and does not perform any type coercion.

Comparing Different Types of R Objects

The identical() function can be used to compare different types of R objects, including vectors, matrices, lists, and data frames.

Let’s illustrate this with a few examples:

1. Matrices:

# Define the matrices
matrix1 <- matrix(1:4, nrow = 2)
matrix2 <- matrix(1:4, nrow = 2)

# Use identical() to compare the matrices
is_identical <- identical(matrix1, matrix2)

# Print the result
print(is_identical)

This will print TRUE, as the two matrices are identical.

2. Lists:

# Define the lists
list1 <- list("apple", "banana", "cherry")
list2 <- list("apple", "banana", "cherry")

# Use identical() to compare the lists
is_identical <- identical(list1, list2)

# Print the result
print(is_identical)

This will print TRUE, as the two lists are identical.

3. Data Frames:

# Define the data frames
df1 <- data.frame("A" = 1:3, "B" = 4:6)
df2 <- data.frame("A" = 1:3, "B" = 4:6)

# Use identical() to compare the data frames
is_identical <- identical(df1, df2)

# Print the result
print(is_identical)

This will print TRUE, as the two data frames are identical.

Taking Attributes into Account

The identical() function also takes into account the attributes of an object. If two objects have the same contents and data type but different attributes, the identical() function will return FALSE.

Let’s illustrate this with an example where we compare two numeric vectors with different names:

# Define the vectors
vector1 <- c(a = 1, b = 2, c = 3)
vector2 <- c(d = 1, e = 2, f = 3)

# Use identical() to compare the vectors
is_identical <- identical(vector1, vector2)

# Print the result
print(is_identical)

When you run this code, the output will be FALSE, as the two vectors have different names.

Conclusion

The identical() function in R is a powerful tool for comparing objects for absolute equality. Unlike the == operator, it tests whether two objects are exactly the same in terms of their contents, their data type, and their attributes.

Remember, the identical() function can be used to compare different types of R objects, including vectors, matrices, lists, and data frames. It can be particularly useful when you need to compare complex objects or when you want to ensure that two objects are exactly the same.