arrange() for sorting in R Programming - Step-by-Step Execution

Concept Flow - arrange() for sorting

Start with data frame

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Call arrange() with column(s)

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Check sorting order

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Reorder rows based on column values

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Return sorted data frame

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End

arrange() takes a data frame and sorts its rows by one or more columns, returning a new sorted data frame.

Execution Sample

R Programming

library(dplyr)
data <- data.frame(name=c('Bob','Alice','Eve'), age=c(25,30,22))
sorted_data <- arrange(data, age)

Sorts the data frame by the 'age' column in ascending order.

Execution Table

Step	Action	Input Data	Sorting Column	Resulting Order	Output
1	Start with original data	[Bob(25), Alice(30), Eve(22)]	-	[Bob, Alice, Eve]	Original data frame
2	Call arrange() on 'age'	[Bob(25), Alice(30), Eve(22)]	age	-	-
3	Compare ages: 25, 30, 22	-	-	-	-
4	Sort rows by age ascending	-	-	[Eve(22), Bob(25), Alice(30)]	-
5	Return sorted data frame	-	-	-	[Eve(22), Bob(25), Alice(30)]

💡 All rows sorted by 'age' ascending, arrange() returns the sorted data frame.

Variable Tracker

Variable	Start	After arrange() call	Final
data	[Bob(25), Alice(30), Eve(22)]	[Bob(25), Alice(30), Eve(22)]	[Bob(25), Alice(30), Eve(22)]
sorted_data	NULL	[Eve(22), Bob(25), Alice(30)]	[Eve(22), Bob(25), Alice(30)]

Key Moments - 2 Insights

Why does arrange() not change the original data frame 'data'?

arrange() returns a new sorted data frame and does not modify the original. See execution_table step 5 where sorted_data is assigned the sorted result, but 'data' remains unchanged.

How does arrange() decide the order when sorting by a column?

arrange() compares the values in the specified column(s) and orders rows from smallest to largest by default, as shown in execution_table step 4.

Visual Quiz - 3 Questions

Look at the execution_table, what is the order of rows after step 4?

A [Eve(22), Bob(25), Alice(30)]

B [Bob(25), Alice(30), Eve(22)]

C [Alice(30), Bob(25), Eve(22)]

D [Eve(22), Alice(30), Bob(25)]

💡 Hint

Check the 'Resulting Order' column in execution_table row 4.

At which step does arrange() compare the values to sort?

A Step 2

B Step 3

C Step 4

D Step 5

💡 Hint

Look at the 'Action' column describing comparison in execution_table.

If we sorted by 'name' instead of 'age', how would the final order change?

A [Eve, Bob, Alice]

B [Bob, Alice, Eve]

C [Alice, Bob, Eve]

D [Alice, Eve, Bob]

💡 Hint

Sorting by 'name' orders alphabetically; check variable_tracker for how sorting changes output.

Concept Snapshot

arrange(data, column1, ...) sorts rows of a data frame by specified columns.
Default order is ascending.
Returns a new sorted data frame; original data unchanged.
Use desc(column) inside arrange() for descending order.
Works with multiple columns for tie-breaking.

Full Transcript

The arrange() function in R sorts a data frame by one or more columns. It takes the original data frame and returns a new one with rows ordered by the values in the specified column(s). The sorting is ascending by default. The original data frame remains unchanged. For example, arranging by age orders rows from youngest to oldest. The process involves comparing values in the sorting column, reordering rows accordingly, and returning the sorted data frame. This visual trace shows each step from starting data, calling arrange(), comparing values, sorting, and returning the result.

Practice

1. What does the arrange() function do in R's dplyr package?

easy

A. Adds new columns to a data frame

B. Filters rows based on a condition

C. Removes duplicate rows from a data frame

D. Sorts rows of a data frame by specified columns

Solution

1. Step 1: Understand the purpose of arrange()

   The arrange() function is used to reorder rows in a data frame based on one or more columns.

2. Step 2: Compare with other functions

   Functions like filter() select rows, mutate() adds columns, and distinct() removes duplicates, so they are different.

3. Final Answer:

   Sorts rows of a data frame by specified columns -> Option D

4. Quick Check:

   arrange() = Sort rows [OK]

Hint: arrange() always changes row order by columns [OK]

Common Mistakes:

• Confusing arrange() with filter()
• Thinking arrange() adds or removes columns
• Assuming arrange() removes duplicates

2. Which of the following is the correct syntax to sort a data frame df by column age in ascending order using arrange()?

easy

A. arrange(df, age)

B. arrange(age, df)

C. arrange(df$age)

D. arrange(df, desc(age))

Solution

1. Step 1: Recall arrange() syntax

   The correct syntax is arrange(data_frame, column_name) to sort by that column ascending.

2. Step 2: Check each option

   arrange(df, age) uses arrange(df, age) which is correct. arrange(age, df) reverses arguments, which is wrong. arrange(df$age) passes a vector, not a data frame. arrange(df, desc(age)) sorts descending, not ascending.

3. Final Answer:

   arrange(df, age) -> Option A

4. Quick Check:

   arrange(data, column) = correct syntax [OK]

Hint: First argument is data frame, second is column name [OK]

Common Mistakes:

• Swapping data frame and column arguments
• Passing column vector instead of data frame
• Using desc() for ascending sort

3. Given the data frame df <- data.frame(name = c('Anna', 'Bob', 'Cara'), score = c(88, 95, 90)), what is the output of arrange(df, desc(score))?

medium

A. Rows sorted by score ascending: Anna, Cara, Bob

B. Rows sorted by score descending: Bob, Cara, Anna

C. Rows sorted by name alphabetically: Anna, Bob, Cara

D. Error because desc() cannot be used inside arrange()

Solution

1. Step 1: Understand desc() inside arrange()

   Using desc(score) sorts the data frame by score in descending order (highest first).

2. Step 2: Apply sorting to given data

   Scores are Anna=88, Bob=95, Cara=90. Descending order is Bob (95), Cara (90), Anna (88).

3. Final Answer:

   Rows sorted by score descending: Bob, Cara, Anna -> Option B

4. Quick Check:

   desc() sorts descending = Bob first [OK]

Hint: desc() reverses sort order inside arrange() [OK]

Common Mistakes:

• Thinking desc() sorts ascending
• Confusing sorting by name vs score
• Believing desc() causes error

4. What is wrong with this code snippet?

arrange(df, desc(age))

where df has no column named age.

medium

A. It will cause an error because age column does not exist

B. It will ignore desc() and sort ascending

C. It will sort by another column automatically

D. It will sort rows by age as NA values

Solution

1. Step 1: Check column existence in arrange()

   arrange() requires the column to exist in the data frame to sort by it.

2. Step 2: Behavior when column missing

   If the column age is missing, R will throw an error indicating the column is not found.

3. Final Answer:

   It will cause an error because age column does not exist -> Option A

4. Quick Check:

   Missing column in arrange() = error [OK]

Hint: arrange() needs existing columns; missing causes error [OK]

Common Mistakes:

• Assuming arrange() ignores missing columns
• Expecting automatic fallback to other columns
• Thinking NA values are sorted without error

5. You have a data frame df with columns city and temperature. How do you sort df first by city alphabetically ascending, then by temperature descending within each city?

hard

A. arrange(df, desc(city), temperature)

B. arrange(df, desc(city), desc(temperature))

C. arrange(df, city, desc(temperature))

D. arrange(df, temperature, city)

Solution

1. Step 1: Understand multi-column sorting with arrange()

   arrange() sorts by columns in the order given. First column sorts primary, second column breaks ties.

2. Step 2: Apply sorting order to columns

   We want city ascending (default) and temperature descending, so use desc(temperature) after city.

3. Final Answer:

   arrange(df, city, desc(temperature)) -> Option C

4. Quick Check:

   Primary city asc, secondary temp desc = arrange(df, city, desc(temperature)) [OK]

Hint: List columns in order; use desc() for descending columns [OK]

Common Mistakes:

• Reversing city sorting with desc() incorrectly
• Sorting temperature ascending instead of descending
• Changing order of columns in arrange()