stringr str_split_n in R: Extract the Nth Piece From a Split

There is no str_split_n() function in stringr. The nth-piece extractor you want is str_split_i() (stringr 1.5+), and the n argument lives on str_split() to cap how many pieces you keep.

str_split_i(x, "/", i = 2)             # nth piece per string, returns vector
str_split_i(x, "/", i = -1)            # last piece per string
str_split(x, "/", n = 2)               # cap at 2 pieces, returns list
str_split_1("a/b/c", "/")[2]           # nth piece from a single string
sapply(str_split(x, "/"), `[`, 2)      # base R fallback before stringr 1.5
str_split_fixed(x, "/", n = 3)[, 2]    # nth column from matrix split
str_split_i(x, fixed("."), i = 1)      # literal dot, not regex

What people mean by str_split_n

str_split_n is a search term, not a function. Two real stringr features cover what searchers usually want:

1. The n argument of str_split(). Caps how many pieces each string is split into. Pieces past n stay joined in the last element.
2. The str_split_i() function. Added in stringr 1.5.0 (2023). Splits each string and returns the i-th piece as a flat character vector, skipping the list-of-vectors detour.

Older blog posts and Stack Overflow answers sometimes used str_split_n as a placeholder for "split and pick the nth piece." The modern, supported answer is str_split_i() for the extraction case, and n = on str_split() for the cap case.

Syntax of str_split_i and the n argument

str_split_i(string, pattern, i) returns a character vector; str_split(string, pattern, n = Inf) returns a list. The first gives you one piece per input. The second controls how many pieces come out per input.

str_split_i() returns three strings (one per input). str_split(..., n = 2) returns a list of length 3, each element a 2-piece vector with the remainder glued into the second slot.

Five common patterns

1. Get the nth piece per string

This is the canonical "give me the nth piece" pattern. One call, vector output, no unlist() or sapply().

2. Get the last piece with negative indexing

Negative i counts from the end. i = -1 is the last piece, i = -2 is second-to-last. Note fixed(".") because a bare "." would be regex and match every character.

3. Cap pieces with the n argument

n = 2 says split at MOST once, even if the delimiter appears again. The first = becomes the boundary; everything after is one value, preserving commas and equals signs inside.

4. Out-of-range i returns NA

str_split_i() returns NA for inputs that do not have the i-th piece. This is safer than positional indexing in a loop, which would error.

5. The base R equivalent

If you cannot upgrade stringr, this is the base R recipe. strsplit() returns a list, then sapply(..., [, n) pulls the nth element from each.

Common pitfalls

Pitfall 1: calling str_split_n directly. Running str_split_n(x, "/", 2) throws could not find function "str_split_n". The function does not exist. Use str_split_i(x, "/", i = 2) instead.

Pitfall 2: bare dot delimiter. str_split_i(files, ".", i = -1) splits on every character because . is regex for "any character." Wrap it in fixed(".") to mean literal dot.

Try it yourself

Related stringr functions

After mastering the nth-piece pattern, look at:

• str_split(): full split, returns a list of vectors
• str_split_1(): split a single string into a vector
• str_split_fixed(): split into a fixed-column matrix
• tidyr::separate_wider_delim(): split a data frame column into named columns
• str_extract(): pull substrings by regex instead of splitting

For data frame columns, separate_wider_delim() is almost always the better tool than mapping str_split_i() across a column.

See the stringr str_split() reference for the full function family on the tidyverse site.

FAQ

Is str_split_n a real function in stringr?

No. There is no str_split_n() in stringr at any version. The closest matches are str_split_i() (returns the i-th piece per string, stringr 1.5+) and the n argument of str_split() (caps how many pieces to return). Calling str_split_n() raises could not find function.

How do I get the nth element from a split in R?

Use str_split_i(x, pattern, i = n). It splits each string and returns the n-th piece as a flat vector. For older stringr or base R, use sapply(strsplit(x, pattern), [, n). Both return one value per input string, with NA where the input has fewer than n pieces.

What does the n argument do in str_split?

n is the maximum number of pieces to split each string into. With n = 2, the first delimiter becomes the split point and the rest of the string stays in the second piece. It is for capping, not for picking; use str_split_i() if you want a specific piece.

How do I split a string and get the last piece?

Use a negative index: str_split_i(x, pattern, i = -1) returns the last piece per string. i = -2 returns second-to-last, and so on. This is cleaner than computing length() for each element first.

What is the difference between str_split_i and str_split_fixed?

str_split_i(x, p, i) returns one piece per input as a flat vector. str_split_fixed(x, p, n) returns ALL pieces as an n-column matrix. Use str_split_i() when you want a single column of results; use str_split_fixed() when you want a full tabular shape.