Variable scope (lexical scoping) in R Programming - Step-by-Step Execution

Concept Flow - Variable scope (lexical scoping)

Start: Global environment

↓

Define function

↓

Call function

↓

Look for variable in function environment

↓

Found?

↓

Use variable

↓

Return value or error if not found

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End

When a function runs, it first looks for variables inside itself. If not found, it looks outside in the environment where it was created, following the chain until found or error.

Execution Sample

R Programming

x <- 10
f <- function() {
  x <- 5
  x
}
f()

Defines x globally as 10, then a function f that has its own x as 5 and returns it. Calling f() returns 5, showing function uses its own x.

Execution Table

Step	Action	Environment	Variable looked up	Value found	Note
1	Assign x <- 10	Global	x	10	Global variable x set to 10
2	Define function f	Global	-	-	Function f created, enclosing environment is Global
3	Call f()	Global -> f	-	-	Function f starts execution
4	Inside f: assign x <- 5	f	x	5	Local variable x set to 5 inside f
5	Inside f: return x	f	x	5	x found locally in f, value 5 returned
6	f() returns	Global	-	5	Function call ends, returns 5

💡 Function f returns local x = 5; global x = 10 is not used inside f

Variable Tracker

Variable	Global Start	After f() call	Inside f after assignment	After f() returns
x	10	10	5 (local in f)	10

Key Moments - 3 Insights

Why does f() return 5 and not 10?

Because inside f(), x is assigned locally to 5 (see execution_table step 4). The function uses its local x, not the global one.

What happens if x is not defined inside f()?

The function looks in the parent environment (global) for x (see concept_flow). If found, it uses that value; otherwise, it gives an error.

Is the global x changed when f() runs?

No, the global x remains 10 (see variable_tracker). The local x inside f() is separate and temporary.

Visual Quiz - 3 Questions

Look at the execution_table step 5. What value of x does f() use to return?

A 10

B 5

C Undefined

D 15

💡 Hint

Check the 'Value found' column at step 5 in execution_table.

At which step does the local variable x get assigned inside the function?

A Step 2

B Step 3

C Step 4

D Step 6

💡 Hint

Look for 'assign x <- 5' in the Action column of execution_table.

If the line 'x <- 5' inside f() was removed, what value would f() return?

A 10

B Error

C 5

D NULL

💡 Hint

Refer to concept_flow: function looks in parent environment if variable not found locally.

Concept Snapshot

Variable scope in R uses lexical scoping.
Functions first look for variables inside themselves.
If not found, they look in the environment where they were created.
Local variables override global ones with the same name.
Global variables remain unchanged by function local assignments.

Full Transcript

This visual trace shows how R uses lexical scoping for variables. We start with a global variable x set to 10. Then we define a function f that assigns x to 5 locally and returns x. When we call f(), it uses the local x inside the function, returning 5, not the global 10. The function looks for variables first inside itself, then outside in the global environment if needed. The global x remains unchanged after calling f(). This helps understand how R finds and uses variables during function execution.