Wide to Long Format

Lesson 9 of 14 in Coddy's Data Manipulation in R course.

In this lesson, we'll focus on using the pivot_longer() function from the tidyr package to convert data from wide to long format.

Understanding Wide and Long Formats

Wide format: Each variable has its own column.
Long format: Variables are stored in key-value pairs, with one column for the variable names and another for the values.

The `pivot_longer()` Function

The pivot_longer() function from tidyr is used to transform data from wide to long format. Here's its basic syntax:

pivot_longer(data, cols, names_to = "key", values_to = "value")

Example:

# Load required library
library(tidyr)

# Create a sample wide format dataset
wide_data <- data.frame(
  name = c("Alice", "Bob", "Charlie"),
  math = c(85, 76, 90),
  science = c(92, 88, 75),
  history = c(78, 82, 85)
)

# Convert to long format
long_data <- pivot_longer(wide_data, 
                          cols = c(math, science, history),
                          names_to = "subject",
                          values_to = "score")

print(long_data)

Output:

# A tibble: 9 × 3
  name    subject score
  <chr>   <chr>   <dbl>
1 Alice   math       85
2 Alice   science    92
3 Alice   history    78
4 Bob     math       76
5 Bob     science    88
6 Bob     history    82
7 Charlie math       90
8 Charlie science    75
9 Charlie history    85

Instead of having 4 columns: name, math, science and history we have 3 columns: name, subject, score

Understanding the Arguments

cols: Specifies which columns to pivot into longer format.
names_to: Names the new column that will contain the column names from the wide format.
values_to: Names the new column that will contain the values.

Importance in Data Analysis

Long format data is often preferred because it's:

Easier to manipulate and analyze with tools like dplyr
More suitable for statistical modeling and visualization
Consistent with the principles of tidy data

Test yourself

This lesson includes a short quiz. Start the lesson to answer it and track your progress.

Test yourself

This lesson includes a short quiz. Start the lesson to answer it and track your progress.

Test yourself

This lesson includes a short quiz. Start the lesson to answer it and track your progress.

Challenge

Easy

Create a function that transforms a wide-format dataset of student exam scores into a long format using the pivot_longer() function from the tidyr package. The function should perform the following operations:

Convert the input string into a data frame
Use pivot_longer() to transform the data from wide to long format
Rename the resulting columns to "subject" and "score"
Arrange the data by student name and then by subject
Print the resulting long-format data frame

Try it yourself

# Read input
con <- file("stdin", "r")
input_string <- suppressWarnings(readLines(con))

# Convert input string to data frame
data <- read.csv(text = input_string, stringsAsFactors = FALSE)

# Load required package
suppressPackageStartupMessages(library(tidyr))
suppressPackageStartupMessages(library(dplyr))

# TODO: Write your code below to transform the data
# Use pivot_longer() to transform from wide to long format
# Rename columns to "subject" and "score"
# Arrange the data by student name and then by subject


# Print the resulting long-format data frame
print(result)