Vector indexing (1-based) in R Programming - Step-by-Step Execution

Concept Flow - Vector indexing (1-based)

Start with vector

↓

Choose index i (1-based)

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Access element at position i

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Return element value

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End

In R, vectors start counting at 1. You pick an index starting from 1 to get the element at that position.

Execution Sample

R Programming

vec <- c(10, 20, 30, 40)
index <- 2
value <- vec[index]
print(value)

This code picks the second element from the vector and prints it.

Execution Table

Step	Variable	Value	Action	Output
1	vec	c(10, 20, 30, 40)	Create vector
2	index	2	Set index to 2
3	value	vec[2]	Access element at position 2	20
4	print(value)		Print the value	20
5			End of execution

💡 Index 2 is valid, so element 20 is returned and printed.

Variable Tracker

Variable	Start	After Step 1	After Step 2	After Step 3	Final
vec	undefined	c(10, 20, 30, 40)	c(10, 20, 30, 40)	c(10, 20, 30, 40)	c(10, 20, 30, 40)
index	undefined	undefined	2	2	2
value	undefined	undefined	undefined	20	20

Key Moments - 3 Insights

Why does R start counting vector positions from 1, not 0?

R uses 1-based indexing, so the first element is at position 1. This is shown in the execution_table where index 2 accesses the second element.

What happens if you try to access vec[0] in R?

Accessing vec[0] returns an empty vector because R does not use zero-based indexing. This differs from some other languages.

Why does vec[2] return 20 and not 10?

Because indexing starts at 1, vec[1] is 10 and vec[2] is 20, as shown in the execution_table step 3.

Visual Quiz - 3 Questions

Look at the execution_table, what is the value of 'value' after step 3?

A 30

B 20

C 10

D undefined

💡 Hint

Check the 'value' variable in the execution_table row for step 3.

At which step is the vector 'vec' created?

A Step 1

B Step 2

C Step 3

D Step 4

💡 Hint

Look at the 'Action' column in the execution_table for vector creation.

If index was set to 3 instead of 2, what would 'value' be after step 3?

A 20

B 40

C 30

D 10

💡 Hint

Refer to the vector elements in variable_tracker and the meaning of index.

Concept Snapshot

Vector indexing in R starts at 1.
Use vec[i] to get the element at position i.
Index 1 is the first element.
Accessing index 0 returns empty.
Always count positions starting from 1.

Full Transcript

This visual trace shows how vector indexing works in R, which uses 1-based counting. We create a vector with four numbers, then pick an index starting at 1. Accessing vec[2] returns the second element, 20. The variable tracker shows how variables change step by step. Key moments clarify why R starts at 1 and what happens if you use zero. The quiz tests understanding of variable values and indexing steps.