Usage of Dollar ($) in R

What is dollar $ in R code and how to use it? Dollar sign $ in R Programming is an operator that is used to access, add, update, and delete elements from the named list, and also it is used to access, add, update, and delete columns from the R Dat aFrame.

The Dollar $ sign in R code is a special operator in R Programming Language that is used to access the List for DataFrame. Similar to bracket [] notation, you can use $ sign to access, add, update and delete variables from list and columns from DataFrame.

2. Using Dollar with List in R

In R, List objects are used to store elements of different types like numbers, strings, vectors, and even lists. The good thing in R is, elements in List can be given names and they can be accessed using these names.

By using the dollar sign in R we can access the list element by name, add elements by name, and update elements.


# Create List
rList <- list(emp_id=c(1,2,3,4,5,6),
           name=c("Smith","Rose","Williams"),
           dept_id=c(10,20,10,10,40,50))

rList

Yields below output. Notice that each element in the list is represented with a $ sign as a prefix to the element name.

2.1 Access Element by Name Using $ Sign

The $ in R allows you to extract or access elements by name from a named list. names() function is used to get the names from the names list. In the following example, I am accessing named elements emp_id and name from the rList object using the $ dollar sign.


# Access named element from list
rList$emp_id
rList$name

Yields below output

2.2 Add New Element to List Using $ Sign

By using the dollar $ sign you can add or insert a new element to the list. In the following example, I am adding dept_name as named list to the rList object. If a named element you are trying to add already exists in the list then it updates the values to the exists list.


# Add new element to the list
rList$dept_name <- c("Finance","Marketing","Sales","IT")
rList

Yields below output. Notice that the new element dept_name has been added to the list.

2.3 Delete Element from List

In order to delete the variable or name from the list assign NULL to the name by referring to using a dollar sign. Fpr example.


# Delete element from list
rList$name <- NULL
rList

I will leave this to you to run and explore the output.

2.4 Accessing Names with Space

Our named list doesn’t have variables with spaces however while referring names by using $ operator, you can try enclosing the name with single quotes. For example.


rList$'dept name' <- c("Finance","Marketing","Sales","IT")
rList$'dept name'

3. Using Dollar with DataFrame in R Code

You can also use dollar sign in R with DataFrame, by using $ sign you can access the column, update the column, add the columnd and delete the column from the DataFrame.

Let’s create an R DataFrame, run these examples and explore the output. If you already have data in CSV you can easily import CSV files to R DataFrame. Also, refer to Import Excel File into R.


# Create emp Data Frame
emp_df=data.frame(
  emp_id=c(1,2,3,4,5,6),
  name=c("Smith","Rose","Williams","Jones","Brown","Brown"),
  dept_id=c(10,20,10,10,40,50)
)
emp_df

# Output
  emp_id     name dept_id
1      1    Smith      10
2      2     Rose      20
3      3 Williams      10
4      4    Jones      10
5      5    Brown      40
6      6    Brown      50

3.1 Add Column to DataFrame

To add a column to the DataFrame, create a vector witht the values and assign it to the DataFrame by using $ sign in R. The following example adds a column dept_branch_id to the Data Frame.


# Add column
emp_df$dept_branch_id <- c(101,102,101,101,104,105)
emp_df

# Output
  emp_id     name dept_id dept_branch_id
1      1    Smith      10            101
2      2     Rose      20            102
3      3 Williams      10            101
4      4    Jones      10            101
5      5    Brown      40            104
6      6    Brown      50            105

3.2 Access Column using Dollar in R

To access the single column from the DataFrame use the $ operator in a form dataframe$columnname. You can also select column by using the bracket notation[] or using select() function from dplyr package.


# Access column
emp_df$dept_branch_id

# Output
# [1] 101 102 101 101 104 105

3.3 Delete Column using Dollar Sign

Similarly, assign NULL to remove the column from DataFrame.


# Delete column
emp_df$dept_branch_id <- NULL
emp_df

# Output
  emp_id     name dept_id
1      1    Smith      10
2      2     Rose      20
3      3 Williams      10
4      4    Jones      10
5      5    Brown      40
6      6    Brown      50

4. Complete Example of Using Dollar in R Code


#Create list
rList <- list(emp_id=c(1,2,3,4,5,6),
           name=c("Smith","Rose","Williams"),
           dept_id=c(10,20,10,10,40,50))
rList

# Access named element from list
rList$emp_id
rList$name

# Add new element to the list
rList$dept_name <- c("Finance","Marketing","Sales","IT")
rList

# Delete element from list
rList$name <- NULL
rList

# Create emp Data Frame
emp_df=data.frame(
  emp_id=c(1,2,3,4,5,6),
  name=c("Smith","Rose","Williams","Jones","Brown","Brown"),
  dept_id=c(10,20,10,10,40,50)
)
emp_df

# Add column
emp_df$dept_branch_id <- c(101,102,101,101,104,105)
emp_df

# Access column
emp_df$dept_branch_id

# Delete column
emp_df$dept_branch_id <- NULL
emp_df

You can also find the complete example at R GitHub Project.

5. Conclusion

In this article, you have learned what is dollar $ operator in R code and by using it how we can access, update, add and element elements from the list. And using $ sign you can also access, update, add and delete columns from DataFrame.

1. What is Dollar Sign in R?