Welcome to the R programming Quiz. Here, you can find 50+ multiple-choice questions (MCQs) covering various aspects of the R programming language. These questions span a wide range of topics within R, including fundamental concepts, syntax, functions, data types, and specific programming practices. Each question is formulated to test understanding and proficiency in R programming, making this collection suitable for learners at different levels, from beginners to intermediate users. The questions also come with answers and brief explanations to reinforce learning and provide insight into the reasoning behind the correct choices.

This set encompasses questions on basic operations, vector manipulation, data frames, functions, control structures, and statistical operations, among others. It's designed to serve as a comprehensive resource for self-assessment, educational purposes, exam preparation, or even as a teaching aid. Whether you're looking to test your understanding of R, prepare for an exam, or construct an educational activity, these MCQs offer a broad overview of the language's capabilities and common programming patterns encountered in data analysis and statistical computing with R.

## 1. What is the use of the *c()* function in R?

### Answer:

### Explanation:

The *c()* function in R is used to combine values into a vector or list. It's a fundamental function for creating vectorized data structures.

## 2. How do you check the structure of an object in R?

### Answer:

### Explanation:

The *str()* function is used to display the structure of an R object, providing a compact, human-readable summary of its type, length, and content.

## 3. Which of the following is used to install packages in R?

### Answer:

### Explanation:

The *install.packages()* function is used to download and install packages from CRAN, making them available for use in R.

## 4. What does the *lapply()* function do?

### Answer:

### Explanation:

The *lapply()* function in R applies a function to each element of a list or vector and returns a list of the same length.

## 5. How do you create a dataframe in R?

### Answer:

### Explanation:

The *data.frame()* function is used to create dataframes in R. Dataframes are used to store tabular data where each column can contain elements of the same or different types.

## 6. Which function is used to read a CSV file into R?

### Answer:

### Explanation:

The *read.csv()* function is used to read a file in CSV (comma-separated values) format and create a dataframe in R.

## 7. What symbol is used to assign a value to a variable in R?

### Answer:

### Explanation:

In R, the *<- i=""> symbol is commonly used for assignment, though = can also be used for the same purpose in many contexts.*

## 8. Which function can be used for generating sequence of numbers in R?

### Answer:

### Explanation:

The *seq()* function is used to generate sequences of numbers in R. It is highly flexible, allowing specification of start, end, and step values.

## 9. What does the *ggplot2* package in R primarily provide?

### Answer:

### Explanation:

The *ggplot2* package is a popular system for creating data visualizations in R, based on the Grammar of Graphics.

## 10. Which of the following functions is used to apply a function to each column of a dataframe or matrix?

### Answer:

### Explanation:

The *apply()* function is used to apply a function to the rows or columns of a matrix or dataframe in R. It is versatile and can operate over arrays as well.

## 11. How do you subset a dataframe in R based on condition?

### Answer:

### Explanation:

The *subset()* function is used for subsetting a dataframe based on a specified condition, making it straightforward to filter rows.

## 12. What is the output type of the *summary()* function when applied to a dataframe?

### Answer:

### Explanation:

When applied to a dataframe, the *summary()* function returns a list that includes summary statistics such as the mean, median, and quartiles for each column.

## 13. Which package in R is most commonly used for data manipulation?

### Answer:

### Explanation:

The *dplyr* package is widely used for data manipulation in R, providing a consistent set of verbs that help in simplifying data manipulation challenges.

## 14. How can you create a scatter plot in R?

### Answer:

### Explanation:

The *plot()* function with type set to "p" creates a scatter plot, where "p" stands for 'points'.

## 15. What does the *t()* function perform on a matrix in R?

### Answer:

### Explanation:

The *t()* function transposes a matrix in R, flipping its rows and columns.

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

### Answer:

### Explanation:

Variable names in R can start with a letter or a dot, but if it starts with a dot, it cannot be followed by a number. An underscore is not a valid starting character for a variable name in R.

## 17. Which data type does NOT exist in R?

### Answer:

### Explanation:

R supports several data types, including character, integer, and complex, but it does not have a data type specifically called 'short'.

## 18. How do you concatenate two strings in R?

### Answer:

### Explanation:

The *paste()* function is used to concatenate strings in R. It can combine multiple strings into one and also allows for the inclusion of a separator.

## 19. How can you define a function in R that calculates the square of a number?

### Answer:

### Explanation:

In R, functions are defined using the *function* keyword, with arguments inside parentheses, followed by the body of the function enclosed in curly braces.

## 20. Which loop structure is NOT present in R?

### Answer:

### Explanation:

R supports *for*, *while*, and *repeat* loops for iteration, but it does not have a *do-while* loop structure.

## 21. Which function is used to create a list containing elements of different types in R?

### Answer:

### Explanation:

The *list()* function is used to create lists in R. Unlike vectors, lists can hold elements of different types.

## 22. How do you define an array with 2 rows and 3 columns in R?

### Answer:

### Explanation:

An array in R can be created using the *array()* function, where the *dim* argument specifies the dimensions of the array.

## 23. What function do you use to add a column to a dataframe in R?

### Answer:

### Explanation:

The *cbind()* function is used to combine objects by columns, which makes it suitable for adding a new column to a dataframe in R.

## 24. How do you access the third element of a vector in R?

### Answer:

### Explanation:

In R, elements of a vector are accessed using square brackets and the index of the element, with indexing starting at 1.

## 25. Which of the following is true about R lists?

### Answer:

### Explanation:

Lists are a versatile data structure in R that can contain elements of different types, including numbers, strings, vectors, and even other lists.

## 26. What is the result of combining a vector of characters and a vector of numbers with the *c()* function?

### Answer:

### Explanation:

When combining characters and numbers using the *c()* function, the numbers are coerced into characters, resulting in a character vector.

## 27. In R, what is the purpose of the *NA* value?

### Answer:

### Explanation:

*NA* is used in R to represent missing or undefined data. It can appear in any type of vector.

## 28. Which function allows you to apply a function conditionally across elements of a list in R?

### Answer:

### Explanation:

The *ifelse()* function evaluates a condition and applies the first function to elements where the condition is true and the second function where it is false. It is vectorized and can be used with lists by applying it within an *lapply()* or *sapply()* function.

## 29. How do you remove NA values from a vector in R?

### Answer:

### Explanation:

To remove NA values from a vector, you can subset the vector by negating the *is.na()* function, which identifies NA values.

## 30. What is the default mode of a vector created by the *vector()* function without specifying the mode?

### Answer:

### Explanation:

If you do not specify the mode when creating a vector with the *vector()* function, it defaults to numeric mode.

## 31. Which R operator is used for element-wise multiplication of two vectors?

### Answer:

### Explanation:

The *** operator performs element-wise multiplication of vectors in R, multiplying each corresponding pair of elements from the two vectors.

## 32. What is the primary way to handle exceptions in R?

### Answer:

### Explanation:

The *try()* function is used in R to handle exceptions, allowing execution to continue even if an error occurs.

## 33. How do you split a string into individual characters in R?

### Answer:

### Explanation:

The *strsplit()* function is used to split strings in R, and providing an empty string as the split parameter splits the string into individual characters.

## 34. Which R function is used to check if a value is NA?

### Answer:

### Explanation:

The *is.na()* function is used to test for missing values (NA) in R. It returns *TRUE* if the value is NA and *FALSE* otherwise.

## 35. How can you repeat a vector *c(1,2,3)* three times in R?

### Answer:

### Explanation:

The *rep()* function repeats the elements of vectors and lists, and the *times* argument specifies how many times to repeat the vector.

## 36. What is the purpose of the *set.seed()* function in R?

### Answer:

### Explanation:

*set.seed()* is used to initialize R's random number generator to a specific state, ensuring reproducibility of code that generates random numbers.

## 37. Which statement creates a factor in R with three levels?

### Answer:

### Explanation:

The *factor()* function is used to encode a vector as a factor, which is useful for categorical data with a fixed number of possible values, or levels.

## 38. How do you convert a factor to a numeric vector in R?

### Answer:

### Explanation:

Converting a factor to a numeric vector directly with *as.numeric()* converts the factor levels to their internal codes. To convert based on the factor's labels, you should first convert it to character with *as.character()* and then to numeric.

## 39. In R, which function can be used to merge two data frames by a common column?

### Answer:

### Explanation:

The *merge()* function merges two data frames by common columns or row names, specified by the *by* argument.

## 40. How is a comment indicated in R code?

### Answer:

### Explanation:

In R, comments are indicated by the *#* symbol. Everything following *#* on the line is treated as a comment.

## 41. Which of the following is a valid way to declare a matrix with 2 rows and 3 columns filled with zeros?

### Answer:

### Explanation:

The *matrix()* function creates a matrix, and its first argument specifies the data to fill the matrix, followed by the *nrow* and *ncol* arguments to specify the number of rows and columns.

## 42. What is the result of the expression *is.vector(list(1,2,3))* in R?

### Answer:

### Explanation:

A list is not considered a vector in R in the context of *is.vector()*, which checks for atomic vectors. Although technically a list is a generic vector, this function specifically returns *FALSE* for lists.

## 43. How can you save the workspace at the end of an R session?

### Answer:

### Explanation:

The *save.image()* function saves the current R workspace to a file, typically called ".RData", allowing you to restore it in future sessions.

## 44. Which of the following functions can be used to generate a sequence that progresses from 1 to 10 in steps of 2 in R?

### Answer:

### Explanation:

The *seq()* function in R is used to generate sequences. The *by* argument specifies the increment between each number in the sequence.

## 45. How do you create a matrix in R where the numbers 1 through 9 are arranged in 3 rows and 3 columns?

### Answer:

### Explanation:

The *matrix()* function creates a matrix from the given set of values. The *nrow* and *ncol* parameters define the number of rows and columns.

## 46. What does the *dim()* function return when applied to a dataframe in R?

### Answer:

### Explanation:

The *dim()* function, when applied to a dataframe, returns a vector of length 2 indicating the number of rows and columns in the dataframe.

## 47. Which of the following syntaxes removes a variable from the R environment?

### Answer:

### Explanation:

The *rm()* function is used to remove objects, such as variables, from the R environment.

## 48. Which function is used to round numbers to the nearest integer in R?

### Answer:

### Explanation:

The *round()* function rounds values to the nearest integer. *floor()* rounds down, and *ceil()* rounds up, while *int()* is not a standard rounding function in R.

## 49. How do you calculate the mean of a numeric vector in R?

### Answer:

### Explanation:

The *mean()* function calculates the arithmetic mean of a numeric vector. While *sum(vector) / length(vector)* could also work, *mean()* is the direct and preferred method.

## 50. Which statement is used to import the *ggplot2* library in an R script?

### Answer:

### Explanation:

The *library()* function is used to load and attach add-on packages. *library(ggplot2)* makes the functions and data in *ggplot2* available for use.

## 51. What is the result of executing *is.logical(c(TRUE, FALSE))* in R?

### Answer:

### Explanation:

*is.logical()* checks if an object is a logical vector. While *c(TRUE, FALSE)* is indeed a logical vector, *is.logical()* checks for the object type, not its content, and a general vector, even solely containing logical values, is considered just a vector, not specifically a logical vector by this function.

## 52. How do you subset a dataframe *df* to only include rows where the value of the column *age* is greater than 30?

### Answer:

### Explanation:

Both the bracket notation with a condition *df[df$age > 30, ]* and the *subset()* function *subset(df, age > 30)* can be used to subset a dataframe based on a condition.

## 53. In R, how can you generate a random sample of 3 numbers from the vector *c(1,2,3,4,5)*?

### Answer:

### Explanation:

The *sample()* function is used for random sampling. Here, it selects 3 random numbers from the provided vector.

## 54. What does the *rnorm()* function generate in R?

### Answer:

### Explanation:

The *rnorm()* function generates random numbers from a normal distribution, with arguments to specify the number of observations, mean, and standard deviation.

## 55. Which keyword is used to define a global variable inside a function in R?

### Answer:

### Explanation:

The *<<-* operator is used to assign a value to a global variable from within a function, altering the variable outside of the function's scope.

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