arrange() for sorting in R Programming - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of arrange() with multiple columns

What is the output of the following R code using dplyr::arrange()?

R Programming

library(dplyr)
df <- tibble(name = c("Anna", "Bob", "Anna", "Bob"), score = c(90, 85, 95, 80))
arranged <- arrange(df, name, desc(score))
print(arranged)

A

name score
1 Bob 80
2 Bob 85
3 Anna 90
4 Anna 95

B

name score
1 Anna 95
2 Anna 90
3 Bob 85
4 Bob 80

C

name score
1 Anna 90
2 Anna 95
3 Bob 80
4 Bob 85

D

name score
1 Bob 85
2 Bob 80
3 Anna 95
4 Anna 90

💡 Hint

Remember that arrange() sorts by the first column ascending, then by the second column descending.

The arrange() function sorts the data frame first by name in ascending order (Anna before Bob), then by score in descending order within each name group.

🧠 Conceptual

intermediate

Understanding arrange() default sorting order

By default, how does arrange() sort the columns in R's dplyr package?

A It does not sort unless specified explicitly.

B It sorts columns in descending order by default.

C It sorts columns randomly by default.

D It sorts columns in ascending order by default.

💡 Hint

Think about the default behavior when no desc() is used.

By default, arrange() sorts columns in ascending order unless wrapped with desc() to reverse the order.

❓ Predict Output

advanced

arrange() with NA values

What is the output of this R code snippet using arrange() when the data contains NA values?

R Programming

library(dplyr)
df <- tibble(x = c(3, NA, 1, 2))
arranged <- arrange(df, x)
print(arranged)

A

x
1 3
2 2
3 1
4 NA

B

x
1 NA
2 1
3 2
4 3

C

x
1 1
2 2
3 3
4 NA

D

x
1 1
2 2
3 NA
4 3

💡 Hint

arrange() puts NA values at the end by default when sorting ascending.

When sorting ascending, arrange() places NA values last.

🔧 Debug

advanced

Identify the error in arrange() usage

What error will this R code produce?

R Programming

library(dplyr)
df <- tibble(a = c(1, 2, 3), b = c(4, 5, 6))
arranged <- arrange(df, c(a, b))
print(arranged)

A Error: Column `c(a, b)` not found

B Error: object 'c' not found

C Error: unexpected ',' in 'arrange(df, c('

D No error, prints sorted dataframe by columns a and b

💡 Hint

arrange() expects columns as separate arguments, not combined in c().

The arrange() function does not accept a vector of columns using c(). It expects columns as separate arguments.

🚀 Application

expert

Sorting a grouped dataframe with arrange()

Given this grouped dataframe, what will be the order of rows after applying arrange(desc(score))?

R Programming

library(dplyr)
df <- tibble(group = c('X', 'X', 'Y', 'Y'), score = c(10, 20, 15, 5))
grouped <- group_by(df, group)
arranged <- arrange(grouped, desc(score))
print(arranged)

A Rows sorted globally by descending score: 20, 15, 10, 5

B Rows sorted within groups by descending score: group X (20, 10), group Y (15, 5)

C Rows sorted within groups by ascending score: group X (10, 20), group Y (5, 15)

D Rows remain in original order because arrange() does not work on grouped data

💡 Hint

arrange() sorts the entire dataframe ignoring groups unless combined with summarise or mutate.

Even if the dataframe is grouped, arrange() sorts all rows globally by the specified column.