Assignment Operators in R (3 Examples) | Comparing = vs. <- vs. <<-

 

On this page you’ll learn how to apply the different assignment operators in the R programming language.

The content of the article is structured as follows:

Let’s dive right into the exemplifying R syntax!

 

Example 1: Why You Should Use <- Instead of = in R

Generally speaking, there is a preference in the R programming community to use an arrow (i.e. <-) instead of an equal sign (i.e. =) for assignment.

In my opinion, it makes a lot of sense to stick to this convention to produce scripts that are easy to read for other R programmers.

However, you should also take care about the spacing when assigning in R. False spacing can even lead to error messages.

For instance, the following R code checks whether x is smaller than minus five due to the false blank between < and -:

my_object1 < -5                # Spaces matter
# Error: object 'my_object1' not found

A properly working assignment could look as follows:

my_object2<-5                  # Hard to read
my_object2                     # Print output
# 5

However, this code is hard to read, since the missing space makes it difficult to differentiate between the different symbols and numbers.

In my opinion, the best way to assign in R is to put a blank before and after the assignment arrow:

my_object3 <- 5                # Easy to read
my_object3                     # Print output
# 5

As mentioned before, the difference between <- and = is mainly due to programming style. However, the following R code using an equal sign would also work:

my_object4 = 5                 # Unconventional code
my_object4                     # Print output
# 5

In the following example, I’ll show a situation where <- and = do not lead to the same result. So keep on reading!

 

Example 2: When <- is Really Different Compared to =

In this Example, I’ll illustrate some substantial differences between assignment arrows and equal signs.

Let’s assume that we want to compute the mean of a vector ranging from 1 to 5. Then, we could use the following R code:

mean(x = 1:5)                  # Does NOT save values in x
# 3

However, if we want to have a look at the vector x that we have used within the mean function, we get an error message:

x
# Error: object 'x' not found

Let’s compare this to exactly the same R code but with assignment arrow instead of an equal sign:

mean(x <- 1:5)                 # Does save values in x
# 3

The output of the mean function is the same. However, the assignment arrow also stored the values in a new data object x:

x                              # Print x
# 1 2 3 4 5

This example shows a meaningful difference between = and <-. While the equal sign doesn’t store the used values outside of a function, the assignment arrow saves them in a new data object that can be used outside the function.

 

Example 3: The Difference Between <- and <<-

So far, we have only compared <- and =. However, there is another assignment method we have to discuss: The double assignment arrow <<- (also called scoping assignment).

The following code illustrates the difference between <- and <<- in R. This difference mainly gets visible when applying user-defined functions.

Let’s manually create a function that contains a single assignment arrow:

my_fun1 <- function() {        # User defined function with <-
  x_fun1 <- 5
}

Now, let’s apply this function in R:

my_fun1()                      # Execute function with <-

The data object x_fun1, to which we have assigned the value 5 within the function, does not exist:

x_fun1                         # Return output of function with <-
# Error: object 'x_fun1' not found

Let’s do the same with a double assignment arrow:

my_fun2 <- function() {        # User defined function with <<-
  x_fun2 <<- 5
}

Let’s apply the function:

my_fun2()                      # Execute function with <<-

And now let’s return the data object x_fun2:

x_fun2                         # Return output of function with <<-
# 5

As you can see based on the previous output of the RStudio console, the assignment via <<- saved the data object in the global environment outside of the user-defined function.

 

Video & Further Resources

I have recently released a video on my YouTube channel, which explains the R syntax of this tutorial. You can find the video below:

 

The YouTube video will be added soon.

 

In addition to the video, I can recommend to have a look at the other articles on this website.

 

In summary: You learned on this page how to use assignment operators in the R programming language. If you have further questions, please let me know in the comments.

assignment-operators-in-r
How to use different assignment operators in R – 3 R programming examples – R programming language tutorial – Actionable R programming syntax in RStudio

 

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