How to Use pivot_longer in tidyr for Data Reshaping

Use pivot_longer() from the tidyr package to convert wide data into a longer format by specifying columns to gather and naming the new key and value columns. It simplifies reshaping data for easier analysis and visualization.

Syntax

The basic syntax of pivot_longer() is:

• data: Your data frame.
• cols: Columns to gather into longer format.
• names_to: Name of the new column that will hold the original column names.
• values_to: Name of the new column that will hold the values from the gathered columns.

r

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

Example

This example shows how to convert a wide data frame with separate columns for years into a long format with year and value columns.

r

library(tidyr)
library(dplyr)

# Sample wide data frame
wide_data <- tibble(
  country = c("USA", "Canada"),
  `2019` = c(100, 80),
  `2020` = c(110, 90),
  `2021` = c(120, 95)
)

# Convert to long format
long_data <- pivot_longer(
  wide_data,
  cols = c(`2019`, `2020`, `2021`),
  names_to = "year",
  values_to = "value"
)

print(long_data)

Output

# A tibble: 6 × 3
  country year  value
  <chr>   <chr> <dbl>
1 USA     2019    100
2 USA     2020    110
3 USA     2021    120
4 Canada  2019     80
5 Canada  2020     90
6 Canada  2021     95

Common Pitfalls

Common mistakes when using pivot_longer() include:

• Not specifying the correct columns in cols, which can cause unexpected columns to be gathered.
• Forgetting to set names_to and values_to, leading to default column names that may be unclear.
• Using non-standard column names without backticks, causing syntax errors.

r

library(tidyr)

# Wrong: missing backticks for numeric column names
# pivot_longer(data, cols = 2019:2021) # This causes error

# Correct usage with backticks
pivot_longer(data, cols = c(`2019`, `2020`, `2021`))

Quick Reference

Argument	Description
data	The data frame to reshape
cols	Columns to pivot into longer format
names_to	Name of the new column for original column names
values_to	Name of the new column for values
names_prefix	Optional prefix to remove from names
values_drop_na	Remove rows with NA values if TRUE

Key Takeaways

Use pivot_longer() to reshape wide data into long format by specifying columns to gather.

Always specify names_to and values_to for clear new column names.

Use backticks around non-standard column names like numbers.

Check that cols argument targets only the columns you want to pivot.

pivot_longer() helps prepare data for easier analysis and plotting.