readr write_delim() in R: Write Data to Delimited Files

The readr write_delim() function saves a data frame to a plain-text file using any field separator you choose. Pass a data frame, a file path, and a delim string to write space, pipe, semicolon, or tab-delimited output.

write_delim(df, "out.txt")                # space-delimited (default)
write_delim(df, "out.psv", delim = "|")   # pipe-delimited
write_delim(df, "out.tsv", delim = "\t")  # tab-delimited
write_delim(df, "out.txt", na = "")       # blank string for missing values
write_delim(df, "out.txt", append = TRUE) # add rows, skip the header
write_delim(df, "out.txt", col_names = FALSE) # write data only, no header
write_delim(df, "out.txt.gz")             # gzip-compressed output (auto-detected)

What write_delim() does

write_delim() is readr's general-purpose text writer. It takes a data frame and serializes each row to a line of text, joining the column values with a delimiter of your choosing. It is the function behind write_csv() and write_tsv(), which are just thin wrappers that fix the delimiter for you.

write_delim() syntax

The signature exposes one required pair and several formatting controls. You must supply x (the data frame) and file (the destination path). Everything else has a default, so the simplest call is two arguments long.

The arguments you will reach for most often:

• delim: the field separator. Defaults to a single space. Set it to "|", ";", or "\t" for other formats.
• na: the string written for NA values. Defaults to "NA"; use "" for a blank cell.
• append: when TRUE, rows are added to an existing file instead of overwriting it.
• col_names: whether to write the header row. Defaults to !append, so headers appear on a fresh write and are skipped when appending.
• quote: when to wrap fields in quotes. "needed" (default) quotes only values that contain the delimiter or a newline.

Writing data with a custom delimiter

The default delimiter is a space, which produces a clean, readable text file. Point write_delim() at any data frame and a path, then read the file back to confirm what landed on disk.

Switch the delimiter with a single argument. Pipe-delimited files are common in data exports because the pipe character rarely appears inside real values, so it avoids the quoting that commas force.

The na argument controls how missing values appear. By default write_delim() writes the literal text NA. Many downstream tools expect a blank or a custom token instead.

Set append = TRUE to grow a file row by row. When appending, col_names defaults to FALSE, so the header is written once and new rows slot in cleanly underneath.

write_delim() vs write_csv() and write_tsv()

Pick the wrapper when the format is standard, and write_delim() when it is not. write_csv() and write_tsv() exist purely for convenience: they call write_delim() with a fixed delimiter and, for CSV, a slightly different default quoting rule.

Common pitfalls

Three mistakes account for most malformed output files.

• Expecting row names. write_delim() never writes data frame row names. The mtcars car names are dropped silently. Move them into a real column with tibble::rownames_to_column() first if you need them.
• Overwriting instead of appending. A plain write_delim() call truncates the file. Forgetting append = TRUE replaces your accumulated data with the latest batch.
• Unquoted delimiters in text. If a character column contains your delimiter, write_delim() quotes that field. Choosing a separator that cannot appear in the data (a pipe, a tab) avoids surprise quotes entirely.

Try it yourself

Related readr functions

These functions cover the rest of the readr write-and-read cycle.

• readr write_csv() writes a standard comma-separated file.
• readr write_tsv() writes a tab-separated file.
• readr read_delim() reads a delimited file back into a data frame.
• write_lines() writes a character vector as plain text lines.
• write_rds() saves an R object in binary form, preserving every attribute.

FAQ

What is the difference between write_delim() and write_csv() in R?

write_csv() is a convenience wrapper that calls write_delim() with delim = ",". Use write_csv() whenever you want a standard comma-separated file, since the name documents your intent. Reach for write_delim() only when you need a non-standard separator such as a pipe, a semicolon, or a space. Both functions write tibbles and plain data frames identically and share the same na, append, and col_names arguments.

How do I write a pipe-delimited file in R?

Call write_delim(df, "file.psv", delim = "|"). The delim argument accepts any single string, so a pipe character produces a pipe-separated file. Pipe delimiters are popular because the character almost never appears inside real data values, which means write_delim() rarely has to add quotes. Read the file back with read_delim("file.psv", delim = "|").

Does write_delim() write row names?

No. write_delim() writes only the columns of the data frame, never the row names. When you write mtcars, the car names disappear from the output. If you need them, promote the row names to a real column first with tibble::rownames_to_column("car"), then write the result.

How do I append data to an existing file with write_delim()?

Pass append = TRUE. The new rows are added below the existing content, and because col_names defaults to !append, the header is skipped automatically. Make sure the delim value matches the delimiter the original file already uses, or the appended rows will not align with the header.

For the official argument reference, see the readr write_delim documentation.