Basic R Programs for Beginners

1.

What is the output of the following R code snippet?

x <- c(1, 2, 3, 4, 5)
y <- c("one", "two", "three", "four", "five")
z <- data.frame(x, y)
summary(z)

A summary of the x and y vectors, including the mean, median, and quartiles of x.

A summary of the x and y vectors, including the number of missing values in each column.

A summary of the z data frame, including the number of observations, the mean, median, and quartiles of x, and the counts and percentages of each unique value of y.

Error

2.

What is the output of the following R code snippet?

x <- c(1, 2, 3, 4, 5)
y <- c("one", "two", "three", "four", "five")
z <- data.frame(x, y)
library(dplyr)
group_by(z, y) %>%
summarize(mean_x = mean(x), sd_x = sd(x))

A data frame with three columns: y, mean_x, and sd_x, containing the unique values of y in the z data frame, along with the mean and standard deviation of the x values for each value of y.

A data frame with two columns: mean_x and sd_x, containing the mean and standard deviation of the x values in the z data frame, grouped by the y values.

An error message, because the group_by function can only be used on numeric columns.

An error message, because the summarize function cannot be used on grouped data.

3.

What is the output of the following R code snippet?

x <- c(1, 2, 3, 4, 5)
y <- sum(x)
print(y)

1

5

15

Error

4.

What is the output of the following R code snippet?

x <- c(1, 2, 3, 4, 5)
y <- c("one", "two", "three", "four", "five")
z <- data.frame(x, y)
library(dplyr)
summarize(z, mean_x = mean(x), sd_x = sd(x))

A data frame with two columns: mean_x and sd_x, containing the mean and standard deviation of the x values in the z data frame.

A data frame with three columns: x, y, and mean_x, containing the original x and y columns, and a new column mean_x with the mean of the x values.

An error message, because the summarize function can only be used on grouped data.

An error message, because the mean and sd functions cannot be used on character columns.

5.

What is the output of the following R code snippet?

x <- c(1, 2, 3, 4, 5)
y <- c(2, 3, 4)
z <- x[!x %in% y]
print(z)

1 2 3

1 5

2 3 4

4 5

6.

What is the output of the following R code snippet?

x <- c(1, 2, 3, 4, 5)
y <- c("one", "two", "three", "four", "five")
z <- data.frame(x, y)
library(ggplot2)
ggplot(z, aes(x = x, y = y)) + geom_point()

A scatterplot with points at the (x, y) coordinates of the data in the z data frame.

A scatterplot with points at the (y, x) coordinates of the data in the z data frame.

An error message, because ggplot2 cannot be used with data frames.

An error message, because geom_point() cannot be used with non-numeric data.

7.

What is the output of the following R code snippet?

x <- c(1, 2, 3, 4, 5)
y <- c("one", "two", "three", "four", "five")
z <- data.frame(x, y)
library(dplyr)
mutate(z, x_squared = x^2)

A data frame with three columns: x, y, and x_squared, containing the original x and y columns, and a new column x_squared with the squares of the x values.

A data frame with two columns: x and y, containing the original x and y columns, and no new columns.

An error message, because the mutate function can only be used on numeric columns.

An error message, because the ^ operator cannot be used on vectors.

8.

What is the output of the following R code snippet?

x <- c(1, 2, 3, 4, 5)
y <- c("one", "two", "three", "four", "five")
z <- data.frame(x, y)
subset(z, x %% 2 == 0)

A data frame with two columns: x and y, with the rows where x is even.

A data frame with two columns: x and y, with the rows where y is even.

A data frame with two columns: x and y, with the rows where both x and y are even.

Error

9.

What is the output of the following R code snippet?

x <- c(1, 2, 3, 4, 5)
y <- c("one", "two", "three", "four", "five")
z <- data.frame(x, y)
library(dplyr)
filter(z, x > 3)

A data frame with two columns: x and y, containing the rows where x is greater than 3.

A data frame with two columns: x and y, containing the rows where y is greater than 3.

A data frame with two columns: x and y, containing the rows where x and y are greater than 3.

Error

10.

What is the output of the following R code snippet?

x <- c(1, 2, 3, 4, 5)
y <- c("one", "two", "three", "four", "five")
z <- data.frame(x, y)
z$y <- as.factor(z$y)
levels(z$y)

1 "2" "3" "4" "5"

one "two" "three" "four" "five"

five "four" "one" "three" "two"

Error