R Loops MCQ

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1. Which loop structure in R is typically used when the number of iterations is known beforehand?

a) while loop
b) for loop
c) repeat loop
d) until loop

Answer:

b) for loop

Explanation:

The for loop in R is commonly used when the number of iterations is known in advance, as it iterates over a sequence or vector of elements.

2. How do you exit a loop prematurely in R?

a) exit()
b) stop()
c) break
d) return

Answer:

c) break

Explanation:

The break statement is used to exit a loop prematurely in R, immediately stopping the loop's execution.

3. What is the syntax to loop through a vector named 'vec' in R?

a) for(i in vec) { }
b) loop(vec) { }
c) for i in vec: { }
d) foreach(i in vec) { }

Answer:

a) for(i in vec) { }

Explanation:

The syntax for looping through a vector in R is 'for(i in vec) { }', where 'i' is the loop variable.

4. What does the 'while' loop in R do?

a) Repeats a block of code while a condition is false
b) Executes a block of code for each element in a sequence
c) Repeats a block of code indefinitely
d) Repeats a block of code while a condition is true

Answer:

d) Repeats a block of code while a condition is true

Explanation:

The while loop in R repeatedly executes a block of code as long as the specified condition remains true.

5. Which loop structure does not inherently have a condition check in R?

a) for loop
b) while loop
c) repeat loop
d) do-while loop

Answer:

c) repeat loop

Explanation:

The repeat loop in R executes indefinitely without an inherent condition check, and it must be manually controlled using a break statement.

6. How do you iterate over the columns of a dataframe 'df' in R?

a) for(col in df) { }
b) for(col in ncol(df)) { }
c) for(col in 1:ncol(df)) { }
d) for(col in colnames(df)) { }

Answer:

c) for(col in 1:ncol(df)) { }

Explanation:

To iterate over the columns of a dataframe 'df', use 'for(col in 1:ncol(df)) { }', where 'col' will be the index of the column.

7. In R, what is the role of the 'next' statement in a loop?

a) To stop the loop execution
b) To skip the current iteration and continue with the next
c) To repeat the current iteration
d) To jump to a specific iteration

Answer:

b) To skip the current iteration and continue with the next

Explanation:

The 'next' statement in a loop in R skips the current iteration and continues with the next iteration of the loop.

8. How can you create an infinite loop in R?

a) for(i in 1:Inf) { }
b) while(TRUE) { }
c) repeat { }
d) Both b and c

Answer:

d) Both b and c

Explanation:

An infinite loop in R can be created using either 'while(TRUE) { }' or 'repeat { }', as these loops do not have a termination condition.

9. What is the typical purpose of a nested loop in R?

a) To execute a loop only once
b) To combine two data sets
c) To perform operations on multi-dimensional data structures
d) To reduce the execution time of loops

Answer:

c) To perform operations on multi-dimensional data structures

Explanation:

Nested loops in R are typically used to perform operations on multi-dimensional data structures, like matrices or data frames.

10. What does a for loop typically consist of in R?

a) Initialization, condition, increment
b) Sequence, body
c) Condition, body
d) Initialization, body, update

Answer:

b) Sequence, body

Explanation:

A for loop in R typically consists of a sequence to iterate over and a body of code that is executed for each element in the sequence.

11. What happens if the condition in a 'while' loop is initially false?

a) The loop executes at least once
b) The loop's body is executed indefinitely
c) The loop's body is not executed at all
d) The loop throws an error

Answer:

c) The loop's body is not executed at all

Explanation:

If the condition in a while loop is initially false, the loop's body does not execute, and the loop ends immediately.

12. How do you ensure a repeat loop eventually terminates in R?

a) Using an if statement with a break
b) By setting a fixed number of iterations
c) By using a countdown timer
d) Repeat loops cannot be terminated

Answer:

a) Using an if statement with a break

Explanation:

To ensure a repeat loop eventually terminates in R, use an if statement with a break condition inside the loop body.

13. Can a for loop be used to iterate over the rows of a matrix in R?

a) Yes, by using 1:nrow(matrix)
b) No, for loops can only iterate over vectors
c) Only with a special package
d) Yes, but only if the matrix has named rows

Answer:

a) Yes, by using 1:nrow(matrix)

Explanation:

A for loop can iterate over the rows of a matrix in R by using the sequence 1:nrow(matrix), where each iteration corresponds to a row.

14. What is the primary advantage of using a loop in R?

a) It reduces the memory usage of a program
b) It makes code execution faster
c) It automates repetitive tasks
d) It simplifies the syntax of complex operations

Answer:

c) It automates repetitive tasks

Explanation:

The primary advantage of using loops in R is to automate repetitive tasks, executing a block of code multiple times.

15. How do you loop through a list of lists in R?

a) Using a for loop with the length() function
b) Using a while loop with an index
c) Using a repeat loop with a counter
d) Lists of lists cannot be looped through in R

Answer:

a) Using a for loop with the length() function

Explanation:

To loop through a list of lists in R, use a for loop with the length() function to iterate over each sublist.

Related MCQ (Multiple Choice Questions) :

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