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)
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.

2.

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

3.

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.

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 <- "Hello"
y <- "World"
z <- paste(x, y)
print(z)

HelloWorld

Hello World

Error

NA

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 = y, y = x)) + geom_boxplot()

A boxplot with boxes at the y-axis labels "one", "two", "three", "four", and "five", with widths corresponding to the x values in the z data frame.

A boxplot with boxes at the x-axis labels "one", "two", "three", "four", and "five", with heights corresponding to the y values in the z data frame.

An error message, because ggplot2 cannot be used with non-numeric data.

An error message, because the geom_boxplot function cannot be used with non-numeric data.

7.

What is the output of the following R code snippet?

x <- 1
while (x < 5) {
print(x)
x <- x + 1
}

1 2 3 4

2 3 4 5

1 2 3 4 5

Error

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)
library(ggplot2)
ggplot(z, aes(x, y)) + geom_point()

A scatterplot of x vs y.

A line plot of x vs y.

A bar plot of x vs y.

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)
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

10.

What is the output of the following R code snippet?

x <- 1
for (i in 1:5) {
x <- x * i
}
print(x)

5

24

120

720