Vector indexing (1-based) in R Programming - Mini Project: Build & Apply

Vector indexing (1-based)

📖 Scenario: You are working with a list of daily temperatures recorded over a week. You want to access specific days' temperatures using their position in the list.

🎯 Goal: Learn how to access elements in a vector using 1-based indexing in R.

📋 What You'll Learn

Create a vector with exact temperature values

Create a variable to hold the index of the day to access

Use vector indexing with the variable to get the temperature

Print the accessed temperature

💡 Why This Matters

🌍 Real World

Accessing specific data points from a list of measurements, like daily temperatures, is common in data analysis and reporting.

💼 Career

Understanding vector indexing is essential for data scientists, statisticians, and anyone working with R for data manipulation.

1

Create the temperature vector

Create a vector called temps with these exact values: 23, 25, 22, 20, 24, 26, 21.

R Programming

# Create the vector temps with the given values
# Your code here

Hint

Use the c() function to create a vector with the given numbers.

2

Set the day index

Create a variable called day_index and set it to 3 to represent the third day.

R Programming

temps <- c(23, 25, 22, 20, 24, 26, 21)
# Create the variable day_index and set it to 3
# Your code here

Hint

Assign the number 3 to the variable day_index.

3

Access the temperature for the day

Create a variable called temp_for_day that gets the temperature from temps at the position given by day_index using vector indexing.

R Programming

temps <- c(23, 25, 22, 20, 24, 26, 21)
day_index <- 3
# Use vector indexing to get the temperature for day_index and store it in temp_for_day
# Your code here

Hint

Use square brackets [] with day_index to get the element from temps.

4

Print the temperature

Print the value of temp_for_day to display the temperature for the third day.

R Programming

temps <- c(23, 25, 22, 20, 24, 26, 21)
day_index <- 3
temp_for_day <- temps[day_index]
# Print the temperature for the day
# Your code here

Hint

Use the print() function to show the value of temp_for_day.

Practice

1. In R, what is the position of the first element in a vector v when using indexing like v[1]?

easy

A. The first element (position 1)

B. The zeroth element (position 0)

C. The last element

D. An error because indexing starts at 0

Solution

1. Step 1: Understand R vector indexing

   R vectors start indexing at 1, not 0 like some other languages.

2. Step 2: Apply indexing to vector v

   Using v[1] selects the first element of the vector.

3. Final Answer:

   The first element (position 1) -> Option A

4. Quick Check:

   R indexing starts at 1 = first element [OK]

Hint: Remember: R indexing always starts at 1, never 0 [OK]

Common Mistakes:

• Thinking indexing starts at 0 like in Python or C
• Confusing position 1 with last element
• Assuming indexing causes an error if 0 is used

2. Which of the following is the correct syntax to get the third element from a vector vec in R?

easy

A. vec[3]

B. vec<3>

C. vec{3}

D. vec(3)

Solution

1. Step 1: Recall R vector indexing syntax

   In R, square brackets [] are used to access elements by position.

2. Step 2: Identify correct syntax for third element

   Using vec[3] correctly accesses the third element.

3. Final Answer:

   vec[3] -> Option A

4. Quick Check:

   Use square brackets for indexing in R [OK]

Hint: Use square brackets [] to index vectors in R [OK]

Common Mistakes:

• Using parentheses () instead of square brackets
• Using curly braces {} which are invalid for indexing
• Using angle brackets <> which are not valid syntax

3. What will be the output of the following R code?

nums <- c(10, 20, 30, 40, 50)
nums[2:4]

medium

A. [10 20 30]

B. [20 30 40]

C. [20 30 40 50]

D. [30 40 50]

Solution

1. Step 1: Understand the vector and indexing range

   The vector nums has elements 10, 20, 30, 40, 50 at positions 1 to 5.

2. Step 2: Extract elements from position 2 to 4

   Using nums[2:4] selects elements at positions 2, 3, and 4 which are 20, 30, and 40.

3. Final Answer:

   [20 30 40] -> Option B

4. Quick Check:

   Positions 2 to 4 = 20, 30, 40 [OK]

Hint: Use colon : to select a range of positions [OK]

Common Mistakes:

• Including position 5 by mistake
• Starting range at 1 instead of 2
• Confusing vector values with positions

4. Consider the R code below. What is the error and how to fix it?

vals <- c(5, 10, 15, 20)
print(vals[0])

medium

A. Error: Use parentheses instead of brackets

B. No error; prints 5

C. Error: Index 0 is invalid; use index starting at 1

D. Error: Vector must be numeric

Solution

1. Step 1: Identify the indexing error

   In R, vector indexing starts at 1; index 0 is invalid and returns an empty vector.

2. Step 2: Correct the index to start at 1

   Replace vals[0] with vals[1] to access the first element.

3. Final Answer:

   Error: Index 0 is invalid; use index starting at 1 -> Option C

4. Quick Check:

   R indexing starts at 1, not 0 [OK]

Hint: Never use 0 as index in R vectors [OK]

Common Mistakes:

• Assuming 0 is a valid index like in other languages
• Trying to use parentheses for indexing
• Thinking vector type causes the error

5. You have a vector data <- c(3, 6, 9, 12, 15). How do you create a new vector containing only the 1st, 3rd, and 5th elements using vector indexing in R?

hard

A. data[1, 3, 5]

B. data[1:3:5]

C. data[c(0, 2, 4)]

D. data[c(1, 3, 5)]

Solution

1. Step 1: Understand how to select multiple elements

   In R, use c() inside square brackets to select multiple positions.

2. Step 2: Apply correct indexing for positions 1, 3, and 5

   Using data[c(1, 3, 5)] selects elements at these positions: 3, 9, and 15.

3. Final Answer:

   data[c(1, 3, 5)] -> Option D

4. Quick Check:

   Use c() inside [] to pick multiple positions [OK]

Hint: Use c() inside [] to select multiple indices [OK]

Common Mistakes:

• Using colon with multiple steps incorrectly
• Using commas inside [] without c()
• Using zero-based indices like 0, 2, 4