For loop in R Programming - Step-by-Step Execution

Concept Flow - For loop

Initialize loop variable i = 1

↓

Check condition: i <= 5?

No→EXIT loop

Yes↓

Execute loop body

↓

Update i: i = i + 1

↩Back to condition check

The loop starts by setting a variable, checks if it meets a condition, runs the code inside if yes, then updates the variable and repeats until the condition is false.

Execution Sample

R Programming

for (i in 1:5) {
  print(i)
}

This code prints numbers from 1 to 5, one number per line.

Execution Table

Iteration	i	Condition (i in 1:5)	Action	Output
1	1	TRUE	print(i)	1
2	2	TRUE	print(i)	2
3	3	TRUE	print(i)	3
4	4	TRUE	print(i)	4
5	5	TRUE	print(i)	5

💡 After iteration 5, the sequence 1:5 is exhausted (no more values), so the loop stops. i remains 5.

Variable Tracker

Variable	Start	After 1	After 2	After 3	After 4	After 5	Final
i	NA	1	2	3	4	5	5

Key Moments - 2 Insights

Why does the loop stop after printing 5?

Because the loop variable i goes from 1 to 5. After i=5, there are no more values in the sequence 1:5, so the loop ends (see execution_table).

Is the loop variable i available after the loop ends?

Yes, in R the variable i still exists after the loop and has the last value it took, which is 5 here (see variable_tracker final value).

Visual Quiz - 3 Questions

Look at the execution_table, what is the value of i during the 3rd iteration?

A 3

B 2

C 4

D 5

💡 Hint

Check the 'i' column in the execution_table row for iteration 3.

How many times does the loop body run?

A 6

B 1

C 5

D 7

💡 Hint

Count the number of rows where Condition is TRUE or Action is 'print(i)' in the execution_table.

If the loop was changed to for(i in 1:3), how many times would the loop body run?

A 5 times

B 3 times

C 6 times

D 1 time

💡 Hint

The loop runs once for each number in the sequence 1:3, check variable_tracker for similar pattern.

Concept Snapshot

for (variable in sequence) {
  # code to repeat
}

- Runs code for each value in sequence
- variable takes each value in order
- Stops after last value
- Loop variable keeps last value after loop

Full Transcript

A for loop in R repeats a block of code for each value in a sequence. It starts by setting a variable to the first value, checks if it is in the sequence, runs the code, then moves to the next value. This continues until all values are used. In the example, the loop prints numbers 1 to 5. The variable i changes from 1 to 5 during the loop and remains 5 after the loop ends because the sequence is exhausted. This shows how the loop controls repetition clearly and simply.