How to Use the source Function in R (With Example)

You can use the source function in R to reuse functions that you create in another R script.

This function uses the following basic syntax:

source("path/to/some/file.R")

Simply add this line to the top of your R script and you’ll be able to use any functions defined in file.R.

The following example shows how to use the source function in practice.

Example: Using the source Function in R

Suppose we have the following R script called some_functions.R that contains two simple user-defined functions:

#define function that divides values by 2
divide_by_two <- function(x) {
  return(x/2)
}

#define function that multiplies values by 3
multiply_by_three <- function(x) {
  return(x*3)
}

Now suppose we’re currently working with some R script called main_script.R.

Assuming some_functions.R and main_script.R are located within the same folder, we can use source at the top of our main_script.R to allow us to use the functions we defined in the some_functions.R script:

source("some_functions.R")

#create data frame
df <- data.frame(team=c('A', 'B', 'C', 'D', 'E', 'F'),
                 points=c(14, 19, 22, 15, 30, 40))

#view data frame
df

  team points
1    A     14
2    B     19
3    C     22
4    D     15
5    E     30
6    F     40

#create new columns using functions from some_functions.R
df$half_points <- divide_by_two(df$points)

df$triple_points <- multiply_by_three(df$points)

#view updated data frame
df

  team points half_points triple_points
1    A     14         7.0            42
2    B     19         9.5            57
3    C     22        11.0            66
4    D     15         7.5            45
5    E     30        15.0            90
6    F     40        20.0           120

Notice that we’re able to create two new columns in our data frame using functions that we defined in the some_functions.R script.

The source function allowed us to use the divide_by_two and multiply_by_three functions in our current script, even though these functions weren’t created in the current script.

Note: In this example, we only used one source function at the top of the file. However, we can use as many source functions as we’d like if we want to reuse functions defined in several different scripts.