How to Use str_pad in R (With Examples)

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str_pad is a function in R, predominantly harnessed from the stringr package, one of the tidyverse packages. It’s primarily used to pad strings to a certain width, thus making it an integral part of string manipulation in R. The function str_pad can pad strings with leading, trailing, or both leading and trailing characters to ensure that the string reaches a specified width.

This article will explore the various applications, nuances, and potential cases where str_pad can be used, along with illustrative examples to facilitate a deeper understanding of the function.

Syntax of str_pad

The basic syntax of the str_pad function is:

str_pad(string, width, side = "right", pad = " ")

Here’s a breakdown of the parameters:

  • string: The input character vector.
  • width: The desired width of the resulting string after padding.
  • side: The side on which padding should be added. It can be “left”, “right”, or “both”.
  • pad: The character used for padding.

Examples of Using str_pad

Example 1: Right Padding

Here’s a simple example where we are padding the string “apple” to a width of 10 characters with the padding on the right side using asterisks (*):


string <- "apple"
padded_string <- str_pad(string, 10, "right", "*")
print(padded_string) # Output: "apple*****"

Example 2: Left Padding

Let’s try padding on the left side of the string “banana”:

string <- "banana"
padded_string <- str_pad(string, 10, "left", "#")
print(padded_string) # Output: "####banana"

Example 3: Both Sides Padding

And here’s how we can add padding to both sides of the string “cherry”:

string <- "cherry"
padded_string <- str_pad(string, 10, "both", "+")
print(padded_string) # Output: "++cherry++"

Advanced Applications and Use-Cases

Using str_pad with Data Frames

str_pad is especially useful when dealing with data frames that contain string variables. For instance, if you have a data frame with a column of product IDs that should all have a uniform width, str_pad can be used to ensure this uniformity.

# Creating a data frame
df <- data.frame(ProductID = c("A1", "B23", "C456"))

# Padding the ProductID column
df$ProductID <- str_pad(df$ProductID, 5, "left", "0")



1     000A1
2     00B23
3     0C456

Conditional Padding

str_pad can be applied conditionally to selectively pad strings based on certain criteria. For instance, you may want to pad strings only if they are below a certain length:

strings <- c("short", "mediumsize", "a very long string")

# Applying conditional padding
padded_strings <- ifelse(nchar(strings) < 10, str_pad(strings, 10, "right", "*"), strings)

# Output:
# [1] "short*****"        "mediumsize"        "a very long string"

Practical Examples and Real-world Scenarios

Aligning Text for Reporting

When generating reports, str_pad can be beneficial to align text efficiently and create an orderly visual representation of data:

names <- c("Apple", "Banana", "Cherry", "Date")
prices <- c(1.23, 0.75, 2.50, 0.30)

# Creating a uniform width for names
names <- str_pad(names, max(nchar(names)), "right", " ")

# Displaying the aligned text
for (i in seq_along(names)) {
  cat(names[i], " - $", prices[i], "\n")


Apple   - $ 1.23 
Banana  - $ 0.75 
Cherry  - $ 2.5 
Date    - $ 0.3 

This code snippet will generate a neat, aligned list of fruit names and their corresponding prices, enhancing the readability of the report.

Formatting Output in Files

str_pad can be instrumental in formatting the output while writing data to text files or logs, ensuring consistent structure and improving the overall aesthetics and readability of the file content.

# Creating and writing a formatted string to a file
output <- str_pad("Error Message:", 20, "right", " ")
writeLines(paste0(output, "Invalid Input"), "log.txt")

This will create a log file with a neatly formatted error message, making it easier to read and analyze.


The str_pad function in R, offered by the stringr package, serves as a versatile tool for string manipulation, allowing users to add padding to strings to ensure they conform to a specified width. From basic applications like aligning text to more advanced and conditional use cases within data frames, str_pad finds extensive usage in a myriad of scenarios.

It is especially useful in real-world scenarios like reporting and formatting output in files where aligned and neatly formatted text is pivotal. While it’s crucial to acknowledge the practicality of str_pad, it’s equally important to leverage it judiciously, considering its performance implications on large-scale data.

By understanding and implementing str_pad effectively, you can enhance the string manipulation capabilities in R, ensuring cleaner, more uniform, and well-organized textual data representation in your analytical endeavors.

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