stringr str_dup() in R: Repeat a String N Times

stringr str_dup() repeats each element of a character vector a fixed number of times and concatenates the copies into one string. It is vectorised, NA aware, and accepts a per-element repeat count, which makes it the standard tool for building separator lines, indentation, and simple text bars.

str_dup("ab", 3)                # "ababab" repeat 3 times
str_dup("-", 20)                # a 20-dash separator line
str_dup(" ", 4)                 # "    " a 4-space indent
str_dup(c("a", "b"), 2)         # "aa" "bb" vectorised
str_dup(c("a", "b"), c(2, 3))   # "aa" "bbb" times varies per element
str_dup("ab", 0)                # "" zero repeats give an empty string
str_dup(NA, 3)                  # NA stays NA (NA-safe)
str_dup("=", n)                 # build a divider n characters wide

What str_dup() does in one sentence

str_dup(string, times) returns a copy of each input element repeated and joined together times times. It works element-wise on a character vector, propagates NA inputs as NA outputs, and accepts a times vector so each element can be repeated a different number of times.

Use str_dup() whenever you need a value made of one repeated unit: a row of dashes for a console rule, a block of spaces for indentation, or a string of symbols for a quick text bar. It is the counterpart to str_c(), which joins several different strings rather than repeating one.

Each element is repeated three times, and the NA input stays NA.

Syntax

str_dup(string, times) takes just two arguments. The first is the character vector to repeat and the second is the number of repeats. There are no side or separator options, so the result is always the input copies pasted directly together.

Because str_dup() is vectorised, times can itself be a vector. When it is, each element of string is repeated by the matching element of times.

Each element is repeated by its matching count, all in a single call.

Five common str_dup() scenarios

Five scenarios cover almost every real use of str_dup(). Each block stands alone so you can paste it straight into the live console.

Build a separator line

The most common use of str_dup() is drawing a divider rule. Repeat a single character to the width you want.

Thirty dashes form a clean horizontal rule for console output or reports.

Indent text with repeated spaces

str_dup() builds indentation by repeating a space. Combine the result with str_c() to prefix any line.

The four-space block can be reused for every nested line, which keeps indentation uniform.

Repeat a column inside a data frame

Most repeating happens inside a tidyverse pipeline. Pass a numeric column as times to repeat a marker per row.

Each row gets a bullet whose length matches its level, which is handy for outline-style displays.

Draw a simple text bar

Repeating a symbol by a count produces a quick text bar chart. This needs no plotting package at all.

Each bar is as long as its count, so a glance at the strings shows the relative sizes.

Repeat a multi-character unit

str_dup() repeats whole strings, not just single characters. Pass a multi-character unit to build a patterned line.

The two-character unit "=-" is repeated five times to produce a ten-character patterned rule.

str_dup() vs strrep() vs paste()

Three functions can repeat a string, but they differ in source and ergonomics. Picking the right one is mostly about whether you want a package dependency.

Reach for str_dup() when you are already using stringr and want a consistent string toolkit, and use base R strrep() when you want the same behaviour without loading a package.

Common pitfalls

Three pitfalls cause most str_dup() surprises. Each has a one-line fix.

Confusing str_dup() with str_c()

str_dup() repeats one string; str_c() joins several different ones. Mixing them up is the most common mistake.

Use str_dup() when the input is a single repeated unit, and use str_c() when you are assembling distinct pieces into one string.

Mismatched lengths in a vectorised call

When both string and times are vectors, their lengths must be compatible. A length that is neither equal nor one raises a recycling error.

Make times either a single value or a vector the same length as string, and the call recycles cleanly.

Forgetting that zero and fractional times are accepted

A times of 0 returns an empty string, and a fractional value is truncated toward zero. Neither raises an error, so a bad count fails silently.

Pass a whole, positive number for times so the result length is exactly what you expect.

Try it yourself

Related stringr functions

When str_dup() is not quite what you need, these are the next stops:

• str_c() joins several different strings end to end, rather than repeating one.
• str_pad() grows a string to a fixed width by adding a pad character on one side.
• str_flatten() collapses a whole vector into a single string with an optional separator.
• str_trunc() shortens strings that exceed a maximum length.
• str_length() counts characters, which helps you pick the right times.
• The full stringr reference documents str_dup() and its arguments.

FAQ

How do I repeat a string multiple times in R?

Use str_dup(string, times) from stringr: str_dup("ab", 3) returns "ababab". The function repeats the input and joins the copies into one string. Because it is vectorised, the same call repeats a whole character vector at once, and times can be a vector so each element is repeated a different number of times.

What is the difference between str_dup() and strrep()?

They do the same job: both repeat each element of a character vector a given number of times and return the joined copies. str_dup() comes from the stringr package and strrep() is built into base R. The results are identical, so the choice is about dependencies. Use str_dup() when you are already working in a stringr or tidyverse pipeline, and use strrep() when you want to avoid loading a package.

How do I create a separator line in R?

Repeat a single character with str_dup(): str_dup("-", 40) returns a 40-dash rule, and str_dup("=", 40) gives a heavier one. Pass the width you want as the times argument. Because str_dup() repeats whole strings, you can also build patterned rules such as str_dup("=-", 20). The result is a plain character string you can print, write to a log, or paste above a heading.

Can str_dup() repeat each element a different number of times?

Yes. The times argument can be a vector the same length as string. str_dup(c("a", "b", "c"), c(1, 2, 3)) returns "a", "bb", and "ccc", repeating each element by its matching count. This is what makes str_dup() useful inside mutate(), where you can pass a numeric column as times to repeat a marker once per row. If the two lengths are incompatible, str_dup() raises a recycling error.

Does str_dup() work with NA values?

Yes, and it is NA-safe. An NA in the string argument produces an NA output, so str_dup(NA, 3) returns NA. An NA in the times argument also returns NA rather than raising an error. This means a missing repeat count can quietly create a missing string, so check times for NA values before the call if a clean result matters.