R Comments

Single-Line Comments

In R, anything after a # symbol on a line is a comment and is ignored by the interpreter. Comments can sit on their own line or follow working code on the same line.

# This line calculates a total
total <- 10 + 5  # inline comment explaining the result
print(total)

Why Use Comments?

• Explain why code does something, not just what it does
• Leave notes for your future self or teammates
• Temporarily disable a line of code while testing
• Document assumptions about the data or the analysis

No True Multi-Line Comment

R does not have a dedicated multi-line comment syntax like /* ... */ found in some other languages. Every commented line needs its own # symbol. Most editors, including RStudio, let you select several lines and comment them all out at once with a keyboard shortcut.

# Step 1: create the data
# Step 2: clean the data
# Step 3: summarize the data
data <- c(1, 2, 3)
print(sum(data))

Commenting Out Code

Adding a # in front of a line of working code is a common way to temporarily disable it without deleting it, which is useful while debugging or trying an alternate approach.