Default argument values in R Programming - Step-by-Step Execution

Concept Flow - Default argument values

Function call

↓

Check arguments

↓

Argument provided?

Yes→Use provided value

↓

No

→Use default value

↓

Run function body with arguments

↓

Return result

When a function is called, R checks if each argument is given. If not, it uses the default value set in the function definition.

Execution Sample

R Programming

add <- function(x, y = 5) {
  return(x + y)
}
add(3)
add(3, 2)

Defines a function with a default value for y, then calls it with and without y.

Execution Table

Step	Function Call	Argument x	Argument y	Used y Value	Calculation	Output
1	add(3)	3	missing	5 (default)	3 + 5	8
2	add(3, 2)	3	2	2 (provided)	3 + 2	5
3	End	-	-	-	-	Function calls complete

💡 No more function calls to execute

Variable Tracker

Variable	Start	Call 1	Call 2	Final
x	undefined	3	3	3
y	undefined	5 (default)	2 (provided)	2 (last call)
result	undefined	8	5	5

Key Moments - 2 Insights

Why does y use 5 in the first call but 2 in the second?

Because in the first call (row 1), y is not provided, so the default 5 is used. In the second call (row 2), y is given as 2, so that value is used instead.

What happens if no default is set and argument is missing?

R will give an error because it expects that argument to be provided. Here, y has a default, so no error occurs.

Visual Quiz - 3 Questions

Look at the execution table, what is the output of add(3)?

A 5

B 8

C 3

D Error

💡 Hint

Check row 1 in the execution_table where add(3) is called and output is shown.

At which step does the function use the default value for y?

A Step 3

B Step 2

C Step 1

D Never

💡 Hint

Look at the 'Used y Value' column in the execution_table for each step.

If we call add(4, 10), what would be the output?

A 14

B 9

C 5

D Error

💡 Hint

Add x and y values; y is provided, so default is ignored.

Concept Snapshot

Function arguments can have default values.
If argument is missing in call, default is used.
If argument is provided, that value is used.
Helps avoid errors and simplify calls.
Syntax: function(arg = default) { ... }

Full Transcript

This example shows how R functions use default argument values. When calling add(3), y is missing, so default 5 is used, resulting in 8. When calling add(3, 2), y is provided as 2, so output is 5. The flow checks if arguments are given; if not, defaults apply. This prevents errors and makes functions flexible.