Sorting with order() in R Programming - Mini Project: Build & Apply

Sorting a List of Fruits by Price Using order() in R

📖 Scenario: You run a small fruit shop and keep a list of fruits with their prices. You want to sort the fruits by their prices to decide which ones to promote.

🎯 Goal: Learn how to use the order() function in R to sort a list of fruits by their prices in ascending order.

📋 What You'll Learn

Create a vector called fruits with the values "apple", "banana", "cherry", "date", "elderberry"

Create a numeric vector called prices with the values 3.5, 2.0, 4.0, 5.5, 1.5

Create a variable called sorted_indices using the order() function on prices

Use sorted_indices to create a new vector called sorted_fruits that sorts fruits by price

Print the sorted_fruits vector

💡 Why This Matters

🌍 Real World

Sorting items by price helps shop owners decide which products to promote or discount.

💼 Career

Understanding sorting techniques is essential for data analysis and organizing information efficiently in many jobs.

1

Create the fruits and prices vectors

Create a vector called fruits with the values "apple", "banana", "cherry", "date", "elderberry". Then create a numeric vector called prices with the values 3.5, 2.0, 4.0, 5.5, 1.5.

R Programming

# Create the fruits vector
# Create the prices vector
# Your code here

Hint

Use the c() function to create vectors in R.

2

Create sorted indices using order()

Create a variable called sorted_indices by using the order() function on the prices vector.

R Programming

fruits <- c("apple", "banana", "cherry", "date", "elderberry")
prices <- c(3.5, 2.0, 4.0, 5.5, 1.5)
# Create sorted_indices using order() on prices
# Your code here

Hint

The order() function returns the positions that would sort the vector.

3

Sort fruits using sorted indices

Create a new vector called sorted_fruits by using sorted_indices to reorder the fruits vector.

R Programming

fruits <- c("apple", "banana", "cherry", "date", "elderberry")
prices <- c(3.5, 2.0, 4.0, 5.5, 1.5)
sorted_indices <- order(prices)
# Use sorted_indices to create sorted_fruits
# Your code here

Hint

Use square brackets [] to reorder a vector by indices.

4

Print the sorted fruits

Print the sorted_fruits vector to display the fruits sorted by price.

R Programming

fruits <- c("apple", "banana", "cherry", "date", "elderberry")
prices <- c(3.5, 2.0, 4.0, 5.5, 1.5)
sorted_indices <- order(prices)
sorted_fruits <- fruits[sorted_indices]
# Print sorted_fruits
# Your code here

Hint

Use the print() function to show the vector.

Practice

1. What does the order() function in R do?

easy

A. Sorts the vector and returns the sorted values directly

B. Removes duplicates from a vector

C. Returns the indices that would sort a vector in ascending order

D. Calculates the sum of all elements in a vector

Solution

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

   The order() function returns the positions (indices) that would sort the vector, not the sorted vector itself.

2. Step 2: Differentiate from sort()

   Unlike sort(), which returns sorted values, order() returns the order of indices to rearrange the vector.

3. Final Answer:

   Returns the indices that would sort a vector in ascending order -> Option C

4. Quick Check:

   order() = indices for sorting [OK]

Hint: Remember: order() gives positions, sort() gives sorted values [OK]

Common Mistakes:

• Confusing order() with sort()
• Expecting order() to return sorted values
• Using order() to remove duplicates

2. Which of the following is the correct syntax to sort a vector v in decreasing order using order()?

easy

A. v[sort(v, decreasing = TRUE)]

B. order(v, decreasing = TRUE)

C. sort(order(v), decreasing = TRUE)

D. v[order(v, decreasing = TRUE)]

Solution

1. Step 1: Use order() with decreasing = TRUE

   To sort vector v in decreasing order, use order(v, decreasing = TRUE) to get indices for sorting from largest to smallest.

2. Step 2: Index vector v with order()

   Use these indices to reorder v as v[order(v, decreasing = TRUE)].

3. Final Answer:

   v[order(v, decreasing = TRUE)] -> Option D

4. Quick Check:

   v[order(v, decreasing=TRUE)] sorts descending [OK]

Hint: Index vector with order() for sorting, add decreasing=TRUE for reverse [OK]

Common Mistakes:

• Using order() without indexing the vector
• Trying to sort order() output directly
• Using sort() on order() output incorrectly

3. What is the output of the following R code?

v <- c(4, 2, 9, 7)
v[order(v)]

medium

A. [1] 2 4 7 9

B. [1] 4 2 9 7

C. [1] 9 7 4 2

D. [1] 2 7 4 9

Solution

1. Step 1: Calculate order(v)

   For v = c(4, 2, 9, 7), order(v) returns indices that sort v: positions of values in ascending order are 2 (2), 1 (4), 4 (7), 3 (9).

2. Step 2: Index v with order(v)

   Using these indices: v[c(2,1,4,3)] gives 2 4 7 9.

3. Final Answer:

   [1] 2 4 7 9 -> Option A

4. Quick Check:

   v[order(v)] = sorted vector ascending [OK]

Hint: order() gives indices to sort; index vector to get sorted values [OK]

Common Mistakes:

• Expecting order() to return sorted values directly
• Mixing up indices and values
• Incorrect indexing order

4. Identify the error in the following R code snippet:

v <- c(5, 3, 8, 1)
sorted_v <- order(v)
print(sorted_v)

medium

A. order() returns indices, not sorted values; should index v with order(v)

B. Missing parentheses in order function call

C. Vector v is not defined before order()

D. print() cannot display vectors

Solution

1. Step 1: Understand what order() returns

   order(v) returns the indices that would sort v, not the sorted vector itself.

2. Step 2: Correct usage to get sorted vector

   To get sorted values, use v[order(v)]. The code assigns indices to sorted_v, so printing it shows positions, not sorted values.

3. Final Answer:

   order() returns indices, not sorted values; should index v with order(v) -> Option A

4. Quick Check:

   order() = indices, index vector to sort [OK]

Hint: Use v[order(v)] to get sorted vector, not order(v) alone [OK]

Common Mistakes:

• Expecting order() to return sorted vector
• Printing order() output directly
• Confusing order() with sort()

5. Given two related vectors names <- c("Anna", "Bob", "Cara") and scores <- c(88, 95, 90), how do you sort names by scores in descending order using order()?

hard

A. order(names, decreasing = TRUE)[scores]

B. names[order(scores, decreasing = TRUE)]

C. scores[order(names, decreasing = TRUE)]

D. sort(names, by = scores, decreasing = TRUE)

Solution

1. Step 1: Use order() on scores with decreasing = TRUE

   To sort names by scores descending, get indices with order(scores, decreasing = TRUE).

2. Step 2: Index names with these order indices

   Use these indices to reorder names: names[order(scores, decreasing = TRUE)].

3. Final Answer:

   names[order(scores, decreasing = TRUE)] -> Option B

4. Quick Check:

   Index names by order(scores, decreasing=TRUE) [OK]

Hint: Sort related vectors by ordering one, index the other [OK]

Common Mistakes:

• Trying to sort names directly by scores without order()
• Using sort() with non-existent 'by' argument
• Mixing order() arguments or indexing incorrectly