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A library for reading and writing CSV files from Clojure

branch: master
README.md

Clojure-CSV

Clojure-CSV is a small library for reading and writing CSV files. The main features:

  • Both common line terminators are accepted.
  • Quoting and escaping inside CSV fields are handled correctly (specifically commas and double-quote characters).
  • Unescaped newlines embedded in CSV fields are supported when parsing.
  • Reading is lazy.
  • More permissive than RFC 4180, although there are some optional strictness checks. (Send me any bugs you find, or any correctness checks you think should be performed.)

This library aims to be as permissive as possible with respect to deviation from the standard, as long as the intention is clear. The only correctness checks made are those that cannot be made after parsing is done. For example, some people think it should be an error when lines in the CSV have a different number of fields -- you should check this yourself. However, it is not possible, after parsing, to tell if the input ended before the closing quote of a field; if you care, it will be signaled to you.

The API has changed in the 2.0 series; see below for details.

Recent Updates

  • Updated library to 2.0.1, which adds the :force-quote option to write-csv. Big thanks to Barrie McGuire for the contribution.
  • Updated library to 2.0.0; essentially identical to 2.0.0-alpha2.

  • Updated library to 2.0.0-alpha2..

  • Rewritten parser for additional speed increases.
  • Benchmarks to help monitor and improve performance.

  • Updated the library to 2.0.0-alpha1.

  • Major update: Massive speed improvements, end-of-line string is configurable for parsing, improved handling of empty files, input to parse-csv is now a string or Reader, and a new API based on keyword args instead of rebinding vars.

Previously...

  • Updated library to 1.3.2.
  • Added support for changing the character used to start and end quoted fields in reading and writing.
  • Updated library to 1.3.1.
  • Fixed the quoting behavior on write, to properly quote any field with a CR. Thanks to Matt Lehman for this fix.
  • Updated library to 1.3.0.
  • Now has support for Clojure 1.3.
  • Some speed improvements to take advantage of Clojure 1.3. Nearly twice as fast in my tests.
  • Updated library to 1.2.4.
  • Added the char-seq multimethod, which provides a variety of implementations for easily creating the char seqs that parse-csv uses on input from various similar objects. Big thanks to Slawek Gwizdowski for this contribution.
  • Includes a bug fix for a problem where a non-comma delimiter was causing incorrect quoting on write.
  • Included a bug fix to make the presence of a double-quote in an unquoted field parse better in non-strict mode. Specifically, if a CSV field is not quoted but has \" characters, they are read as \" with no further processing. Does not start quoting.
  • Reorganized namespaces to fit better with my perception of Clojure standards. Specifically, the main namespace is now clojure-csv.core.
  • Significantly faster on parsing. There should be additional speed improvements possible when Clojure 1.2 is released.
  • Support for more error checking with *strict* var.
  • Numerous bug fixes.

Obtaining

If you are using Leiningen, you can simply add

[clojure-csv/clojure-csv "2.0.1"]

to your project.clj and download it from Clojars with

lein deps

Use

The clojure-csv.core namespace exposes two functions to the user:

parse-csv

Takes a CSV as a char sequence or string, and returns a lazy sequence of vectors of strings; each vector corresponds to a row, and each string is one field from that row. Be careful to ensure that if you read lazily from a file or some other resource that it remains open when the sequence is consumed.

Takes the following keyword arguments to change parsing behavior:

:delimiter

A character that contains the cell separator for each column in a row.

Default value: \,

:end-of-line

A string containing the end-of-line character for reading CSV files. If this setting is nil then \n and \r\n are both accepted.

Default value: nil

:quote-char

A character that is used to begin and end a quoted cell.

Default value: \"

:strict

If this variable is true, the parser will throw an exception on parse errors that are recoverable but not to spec or otherwise nonsensical.

Default value: false

write-csv

Takes a sequence of sequences of strings, basically a table of strings, and renders that table into a string in CSV format. You can easily call this function repeatedly row-by-row and concatenate the results yourself.

Takes the following keyword arguments to change the written file:

:delimiter

A character that contains the cell separator for each column in a row.

Default value: \,

:end-of-line

A string containing the end-of-line character for writing CSV files.

Default value: \n

:quote-char

A character that is used to begin and end a quoted cell.

Default value: \"

:force-quote

If this variable is true, the output will have ever field quoted, whether this is needed or not. This can apparently be helpful for interoperating with Excel.

Default value: false

Changes from API 1.0

Clojure-CSV was originally written for Clojure 1.0, before many of the modern features we now enjoy in Clojure, like keyword args, an IO library and fast primitive math. The 2.0 series freshens up the API to more modern Clojure API style, language capabilities, and coding conventions. The JARs for the 1.0 series will remain available indefinitely (probably a long, long time), so if you can't handle an API change, you can continue to use it as you always have.

Here's a summary of the changes:

  • Options are now set through keyword args to parse-csv and write-csv. The dynamic vars are removed.
    • Rationale: Dynamic vars are a little annoying to rebind. This can tempt you to imprudently set them for too wide a swath of code. Reusing the same vars for both reading and writing meant that the vars had to have the same meaning in each context, or else two vars introduced to accommodate the differences. Keyword args are clear, fast, explicit, and local.
  • Parsing logic is now based on Java readers instead of Clojure char seqs.
    • Rationale: Largely performance. Clojure's char seqs are not particularly fast and throw off a lot of garbage. It's not clear that working entirely with pure Clojure data structures was providing much value to anyone. When you're doing IO, Readers are close at hand in Java, and now the basis for Clojure's IO libs.
  • An empty file now parses as a file with no rows.
    • Rationale: The CSV standard actually doesn't say anything about an input that is an empty file. Clojure-CSV 1.0 would return a single row with an empty string in it. The logic was that a CSV file row is everything between the start of a line and the end of the line, where an EOF is a line terminator. This would mean an empty file is a single row that has an empty field. An alternative, and equally valid view is that if a file has nothing in it, there is no row to be had. A file that is a single row with an empty field can still be expressed in this viewpoint as a file that contains only a line terminator. The same cannot be said of the 1.0 view of things: there was no way to represent a file with no rows. In any case, I went and looked at many other CSV parsing libraries for other languages, and they universally took the view that an empty CSV file has no rows, so now Clojure-CSV does as well.
  • The end-of-line option can now be set during parsing. If end-of-line is set to something other than nil, parse-csv will treat \n and \r\n as any other character and only use the string given in end-of-line as the newline.

Bugs

Please let me know of any problems you are having.

Contributors

License

Eclipse Public License

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