R is a versatile language primarily used for statistical analysis and data visualization. With its extensive library support and flexibility, R has cemented its place as an essential tool for data scientists and researchers. Dive into this set of 25 multiple-choice questions to test and expand your R programming knowledge!

## 1. What is R primarily used for?

### Answer:

### Explanation:

While R can have other applications, its primary use is for statistics and data visualization.

## 2. Which function is used to install packages in R?

### Answer:

### Explanation:

install.packages() is used to install new packages in R. The other functions are used to load or check packages.

## 3. How do you load a package in R?

### Answer:

### Explanation:

require() is used to load a package in R. If the package isn't installed, it returns FALSE.

## 4. What is the correct way to load the ggplot2 package?

### Answer:

### Explanation:

Both require("ggplot2") and library(ggplot2) are correct methods to load the ggplot2 package in R.

## 5. Which data structure in R can hold elements of different types?

### Answer:

### Explanation:

Lists in R can hold elements of different types, while vectors, matrices, and arrays hold elements of the same type.

## 6. How do you create a vector c(1,2,3,4) in R?

### Answer:

### Explanation:

Both 1:4 and v = c(1,2,3,4) create the desired vector.

## 7. In R, what is the output of the expression c(1,2,3) + c(1,1,1)?

### Answer:

### Explanation:

Vector addition in R is element-wise, so 1+1=2, 2+1=3, and 3+1=4.

## 8. Which function is used to check if an R package is installed?

### Answer:

### Explanation:

While require() primarily loads a package, it returns FALSE if the package isn't installed, effectively checking its presence.

## 9. Which of the following is NOT a valid variable name in R?

### Answer:

### Explanation:

Variable names in R cannot start with a number.

## 10. Which base R function provides the structure of an R object?

### Answer:

### Explanation:

str() gives the structure of an R object, detailing the type, length, and content.

## 11. What is the default data visualization package in R?

### Answer:

### Explanation:

R's base graphics system is the default plotting system.

## 12. What does the apply() function do in R?

### Answer:

### Explanation:

apply() is used to apply a function across rows or columns of a matrix.

## 13. Which function is used to combine multiple vectors into a data frame?

### Answer:

### Explanation:

data.frame() is used to combine multiple vectors into a single data frame.

## 14. What is the output of class(NA) in R?

### Answer:

### Explanation:

By default, NA (representing missing data) is of the logical type.

## 15. Which R function is used for statistical hypothesis tests?

### Answer:

### Explanation:

t.test() is a commonly used function for t-tests, which are types of statistical hypothesis tests.

## 16. Which function in R is used to seed the random number generator to ensure reproducibility?

### Answer:

### Explanation:

set.seed() initializes the random number generator, ensuring consistent and reproducible results.

## 17. What does the rnorm() function do in R?

### Answer:

### Explanation:

rnorm() generates random numbers following a normal distribution.

## 18. How do you access the second element of a list named my_list?

### Answer:

### Explanation:

Lists in R are accessed using double square brackets.

## 19. Which of the following is true about R's data frames?

### Answer:

### Explanation:

In R's data frames, each row is an observation and each column is a variable or feature.

## 20. Which R function is used to handle exceptions?

### Answer:

### Explanation:

tryCatch() provides exception handling by capturing errors and allowing for recovery actions.

## 21. Which of the following R functions is used to get the class of an object?

### Answer:

### Explanation:

In R, both class() and typeof() provide information about the type or class of an object, but they can sometimes return different results based on the underlying data structure.

## 22. Which base R function returns a logical vector indicating if each element is missing?

### Answer:

### Explanation:

is.na() checks each element of an object and returns a logical vector indicating if the elements are NA (missing).

## 23. What does the lapply() function return?

### Answer:

### Explanation:

lapply() returns a list of the same length as the input. It applies a function to each element of a list or vector.

## 24. Which R function is used to export data frames to .csv files?

### Answer:

### Explanation:

write.csv() is the function used to write a data frame to a .csv file in R.

## 25. How do you subset rows of a data frame df where the column 'age' is greater than 30?

### Answer:

### Explanation:

Both df[df$age > 30, ] and subset(df, age > 30) are valid methods to subset rows based on a condition in R.