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R Academy · Lesson

Formatted Output with sprintf()

Control decimal places, padding, and alignment with sprintf format strings.

Formatted Output with sprintf() is a free R Academy lesson on CoddyKit — lesson 2 of 4. You can read the complete lesson below for free — then practise it hands-on in the browser with a built-in code editor and a 24/7 AI tutor. It is part of the R Academy learning path, one of 4 lessons in the course, and your progress syncs across the web and the CoddyKit app.

sprintf() Basics

sprintf() formats strings using a format string with placeholders. It works exactly like C's printf. The first argument is the format template; subsequent arguments fill the placeholders in order.

sprintf('There are %d items', 5)
sprintf('Hello, %s!', 'Alice')
sprintf('Price: %.2f', 9.999)

Integer and String Placeholders

%d formats an integer, %s formats a string, and %f formats a floating-point number. Each placeholder is replaced in order by the corresponding argument.

name <- 'Bob'
age  <- 34
score <- 88.5
sprintf('%s is %d years old with score %.1f', name, age, score)

Controlling Decimal Places

%.2f means: format as float with exactly 2 decimal places. The number between . and f controls precision. This is ideal for currency, percentages, and scientific values.

pi_val <- 3.14159265
sprintf('%.0f', pi_val)
sprintf('%.2f', pi_val)
sprintf('%.5f', pi_val)
sprintf('$%.2f', 1234.5)

Field Width and Padding

A number before the format letter sets the minimum field width. Values are right-aligned by default, padded with spaces on the left. This is useful for aligning columns in plain-text reports.

items <- c('Pen', 'Notebook', 'Stapler')
prices <- c(1.5, 4.99, 7.25)
for (i in seq_along(items)) {
  cat(sprintf('%-10s $%6.2f\n', items[i], prices[i]))
}

Left-Alignment with the - Flag

Prefix the width number with - to left-align text within the field. This is the standard way to produce left-justified columns in fixed-width text output.

# Right-aligned (default)
sprintf('%10s', 'hi')
# Left-aligned
sprintf('%-10s', 'hi')
# Practical: side-by-side
cat(sprintf('%-8s %5d\n', 'Alice', 42))
cat(sprintf('%-8s %5d\n', 'Bob', 7))

Scientific Notation with %e and %g

%e forces scientific notation (e.g. 1.23e+04). %g automatically chooses the shorter of %f or %e — useful when values span many orders of magnitude.

x <- 0.000123456
y <- 123456789
sprintf('%e', x)
sprintf('%e', y)
sprintf('%g', x)
sprintf('%g', y)

Zero Padding with 0 Flag

Prefix the width with 0 to pad numbers with leading zeros instead of spaces. This is commonly used for zero-padded IDs, dates, and file numbering schemes.

ids <- c(1, 12, 123, 1234)
sprintf('ID_%05d', ids)
# Date parts
sprintf('%04d-%02d-%02d', 2024, 5, 7)

Percentage Formatting

To display a ratio as a percentage, multiply by 100 and use %.1f%%. The double %% inserts a literal percent sign in the output (a single % would be interpreted as the start of a placeholder).

pass_rate <- 0.8743
sprintf('Pass rate: %.1f%%', pass_rate * 100)
growth <- 0.0523
sprintf('Growth: +%.2f%%', growth * 100)

sprintf() is Vectorized

When you pass a vector as an argument to sprintf(), it automatically iterates over the vector and returns one formatted string per element. The format string itself is recycled.

products <- c('Apple', 'Banana', 'Cherry')
prices   <- c(0.99, 0.59, 2.49)
sprintf('%-8s costs $%.2f', products, prices)

Multiple Placeholders, Multiple Arguments

Each placeholder consumes one argument in order. You can mix %d, %f, and %s freely in a single format string, and all vector arguments are recycled to the longest length.

months <- c('Jan', 'Feb', 'Mar')
revenue <- c(12500, 9800, 15300)
growth  <- c(0.05, -0.12, 0.18)
sprintf('%s: $%d (growth: %+.1f%%)',
        months, revenue, growth * 100)

sprintf() vs paste() — When to Use Each

Use paste()/paste0() for simple concatenation; use sprintf() when you need precise numeric formatting (decimal places, widths, padding). sprintf() is more verbose but gives you complete control over number appearance.

val <- 1234567.891
# paste: no formatting control
paste('Total:', val)
# sprintf: formatted as currency
sprintf('Total: $%,.2f', val)
# With manual formatting
sprintf('Total: $%15.2f', val)

Quick Check

Which format code in sprintf() inserts a literal percent sign % into the output?

sprintf() Key Takeaways

Key takeaways for sprintf():

  • %d integer, %f float, %s string, %e scientific, %g auto
  • %.2f = 2 decimal places; %10.2f = width 10, 2 decimals
  • %-10s = left-align in 10-char field; %05d = zero-pad to 5 digits
  • %% = literal percent sign in output
  • sprintf() is vectorized over its arguments
  • Prefer sprintf() over paste() when numeric formatting precision matters
x <- 0.87654
cat(sprintf('Default f  : %f\n', x))
cat(sprintf('2 decimals : %.2f\n', x))
cat(sprintf('Percentage : %.1f%%\n', x * 100))
cat(sprintf('Scientific : %e\n', x))
cat(sprintf('Auto       : %g\n', x))

Frequently asked questions

Is the “Formatted Output with sprintf()” lesson free?

Yes — the full text of “Formatted Output with sprintf()” is free to read here on the web, and the R Academy course includes 4 lessons in total. To practise it interactively (a built-in code editor and a 24/7 AI tutor) and unlock the rest of the R Academy course, upgrade to CoddyKit PRO.

What will I learn in “Formatted Output with sprintf()”?

Control decimal places, padding, and alignment with sprintf format strings. You practise R Academy with hands-on code you run directly in the browser, and a 24/7 AI tutor answers your questions as you work through the lesson.

Do I need any experience to start R Academy?

No prior experience is required. R Academy on CoddyKit is structured for beginners through advanced learners; this is — lesson 2 of 4, so you can start here or from the beginning and move at your own pace.

How long does the “Formatted Output with sprintf()” lesson take?

Most CoddyKit lessons take about 5–10 minutes. Each one is bite-sized and interactive, so you make steady progress and pick up exactly where you left off across the web and the app.

Can I write and run code in this R Academy lesson?

Yes. Every R Academy lesson includes a built-in code editor, so you write and run real code right in your browser and get instant AI feedback — no local setup required.

All lessons in this course

  1. Building Strings with paste() and paste0()
  2. Formatted Output with sprintf()
  3. Displaying Output with cat() and print()
  4. String Padding and Alignment
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