For loop in R Programming - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of a simple for loop with sequence

What is the output of this R code?

result <- c()
for (i in 1:4) {
  result <- c(result, i * 2)
}
print(result)

R Programming

result <- c()
for (i in 1:4) {
  result <- c(result, i * 2)
}
print(result)

A [1] 1 2 3 4

B [1] 2 3 4 5

C [1] 4 8 12 16

D [1] 2 4 6 8

💡 Hint

Remember the loop multiplies each number by 2 before adding to the result.

The loop runs from 1 to 4, multiplying each number by 2 and adding it to the result vector. So the output is 2, 4, 6, 8.

❓ Predict Output

intermediate

Output of nested for loops with sum

What is the output of this R code?

total <- 0
for (i in 1:2) {
  for (j in 1:3) {
    total <- total + i + j
  }
}
print(total)

R Programming

total <- 0
for (i in 1:2) {
  for (j in 1:3) {
    total <- total + i + j
  }
}
print(total)

A [1] 18

B [1] 21

C [1] 12

D [1] 15

💡 Hint

Add all pairs of i and j from the loops.

The sums are: (1+1)+(1+2)+(1+3)+(2+1)+(2+2)+(2+3) = 2+3+4+3+4+5 = 21. But the code adds i+j each iteration to total, so total is 21.

🔧 Debug

advanced

Identify the error in this for loop

What error does this R code produce?

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

R Programming

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

A SyntaxError: unexpected symbol 'i'

B Error: object 'i' not found

C Error: unexpected '{' in "for i in 1:5 {"

D No error, prints numbers 1 to 5

💡 Hint

Check the syntax of the for loop header in R.

In R, the for loop syntax requires parentheses around the loop variable and sequence: for (i in 1:5) {...}. Missing parentheses cause a syntax error at '{'.

❓ Predict Output

advanced

Output of for loop with conditional break

What is the output of this R code?

result <- c()
for (i in 1:10) {
  if (i > 4) {
    break
  }
  result <- c(result, i)
}
print(result)

R Programming

result <- c()
for (i in 1:10) {
  if (i > 4) {
    break
  }
  result <- c(result, i)
}
print(result)

A [1] 1 2 3 4

B [1] 1 2 3 4 5

C [1] 1 2 3

D [1] 5 6 7 8 9 10

💡 Hint

The loop stops when i is greater than 4.

The loop adds numbers 1 to 4 to result. When i becomes 5, the break stops the loop, so 5 is not added.

🧠 Conceptual

expert

Number of iterations in a for loop with sequence and step

How many times will this R for loop run?

count <- 0
for (i in seq(2, 10, by=3)) {
  count <- count + 1
}
print(count)

R Programming

count <- 0
for (i in seq(2, 10, by=3)) {
  count <- count + 1
}
print(count)

A 3

B 2

C 5

D 4

💡 Hint

Check the sequence generated by seq(2, 10, by=3).

seq(2, 10, by=3) generates 2, 5, 8. So the loop runs 3 times.