CSV Module

This XQuery Module contains a single function to parse CSV input. CSV (comma-separated values) is a popular representation for tabular data, exported e. g. from Excel.

Conventions

All functions in this module are assigned to the http://basex.org/modules/csv namespace, which is statically bound to the csv prefix.
All errors are assigned to the http://basex.org/errors namespace, which is statically bound to the bxerr prefix.

Conversion

XML: Direct, Attributes

CSV is converted to XML as follows:

• The resulting XML document has a <csv> root element.
• Rows are represented via <record> elements.
• Fields are represented via <entry> elements. The value of a field is represented as text node.
• If the header option is set to true, the first text line is parsed as table header, and the <entry> elements are replaced with the field names:
  • Empty names are represented by a single underscore (_), and characters that are not valid in element names are replaced with underscores or (when invalid as first character of an element name) prefixed with an underscore.
  • If the lax option is set to false, invalid characters will be rewritten to an underscore and the character’s four-digit Unicode, and underscores will be represented as two underscores (__). The resulting element names may be less readable, but can always be converted back to the original field names.
• If format is set to attributes, field names will be stored in name attributes.

A little advice: in the Database Creation dialog of the GUI, if you select CSV Parsing and switch to the Parsing tab, you can see the effects of some of the conversion options.

XQuery

Template:Mark:

CSV records can be converted to a plain sequence of arrays:

• The resulting value will be a map with a records and an optional names key.
• Records are organized as a sequence of arrays. A single array contains the entries of a single record.
• The column names will be available if header option is set to true.

The resulting data can e.g. be accessed as follows:

• $csv?records[5] returns all entries of the 5th record (row)
• $csv?records(2) returns all entries of the 2nd field (column)
• $csv?names?* returns the names of all fields (if available)
• Return string representation for each record:

for $record at $pos in $csv?records
return $pos || ". " || string-join($record?*, ', ')

The resulting representation consumes less memory than XML-based formats, and values can be directly accessed without conversion. Thus, it is recommendable for very large inputs and for efficient ad-hoc processing. Before Version 9.0, a map format was available, which was now replaced with the more flexible and light-weight xquery format.

Options

In the following table, all available options are listed. The Excel column indicates what are the preferred options for data that is to be imported, or has been exported from Excel.

Option	Description	Allowed	Default	Excel
separator	Defines the character which separates the values of a single record.	comma, semicolon, colon, tab, space or a single character	comma	semicolon
header	Indicates if the first line of the parsed or serialized CSV data is a table header.	yes, no	no
format	Specifies the format of the XML data: With direct conversion, field names are represented as element names With attributes conversion, field names are stored in name attributes With xquery conversion, the input is converted to an XQuery map	direct, attributes, map	direct
lax	Specifies if a lax approach is used to convert QNames to JSON names.	yes, no	yes	no
quotes	Specifies how quotes are parsed: Parsing: If the option is enabled, quotes at the start and end of a value will be treated as control characters. Separators and newlines within the quotes will be adopted without change. Serialization: If the option is enabled, the value will be wrapped with quotes. A quote character in the value will be encoded according to the rules of the backslashes option.	yes, no	yes	yes
backslashes	Specifies how quotes and other characters are escaped: Parsing: If the option is enabled, \r, n and \t will be replaced with the corresponding control characters. All other escaped characters will be adopted as literals (e.g.: \" → "). If the option is disabled, two consecutive quotes will be replaced with a single quote (unless quotes is enabled and the quote is the first or last character of a value). Serialization: If the option is enabled, \r, n, \t, " and the separator character will be encoded with a backslash. If the option is disabled, quotes will be duplicated.	yes, no	no	no

Functions

csv:parse

Signatures	csv:parse($input as xs:string) as document-node(element(csv)) csv:parse($input as xs:string, $options as map(xs:string, item())) as item()
Summary	Converts the CSV data specified by $input to an XML document or a map. The $options argument can be used to control the way the input is converted.
Errors	BXCS0001: the input cannot be parsed.

csv:serialize

Signatures	csv:serialize($input as node()) as xs:string csv:serialize($input as node(), $options as map(xs:string, item())) as xs:string
Summary	Serializes the node specified by $input as CSV data, and returns the result as xs:string. Items can also be serialized as JSON if the Serialization Parameter method is set to csv. The $options argument can be used to control the way the input is serialized.
Errors	BXCS0002: the input cannot be serialized.

Examples

Example 1: Converts CSV data to XML, interpreting the first row as table header:

Input addressbook.csv:

Name,First Name,Address,City
Huber,Sepp,Hauptstraße 13,93547 Hintertupfing

Query:

let $text := file:read-text('addressbook.csv')
return csv:parse($text, map { 'header': true() })

Result:

<csv>
  <record>
    <Name>Huber</Name>
    <First_Name>Sepp</First_Name>
    <Address>Hauptstraße 13</Address>
    <City>93547 Hintertupfing</City>
  </record>
</csv>

Example 2: Converts some CSV data to XML and back, and checks if the input and output are equal. The expected result is true:

Query:

let $options := map { 'lax': false() }
let $input := file:read-text('some-data.csv')
let $output := $input => csv:parse($options) => csv:serialize($options)
return $input eq $output

Example 3: Converts CSV data to XQuery and returns distinct column values:

Query:

let $text := ``[Name,City
Jack,Chicago
Jack,Washington
John,New York
]``
let $options := map { 'format': 'xquery', 'header': true() }
let $data := csv:parse($text, $options)
return (
  'Distinct values:',
  let $records := $data?records
  for $name at $pos in $data?names?*
  let $values := $records?($pos)
  return (
    '* ' || $name || ': ' || string-join(distinct-values($values), ', ')
  )
)

Result:

Distinct values:
* Name: Jack, John
* City: Chicago, Washington, New York

Errors

Code	Description
BXCS0001	The input cannot be parsed.
BXCS0002	The node cannot be serialized.

Changelog

Version 9.0

• Added: xquery option
• Removed: map option

Version 8.6

• Updated: Options: improved Excel compatibility

Version 8.0

• Added: backslashes option

Version 7.8

• Updated: csv:parse now returns a document node instead of an element, or an XQuery map if format is set to map.
• Added: format and lax options

The module was introduced with Version 7.7.2.