Difference between revisions of "CSV Module"
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=Conventions= | =Conventions= | ||
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All functions and errors in this module are assigned to the <code><nowiki>http://basex.org/modules/csv</nowiki></code> namespace, which is statically bound to the {{Code|csv}} prefix.<br/> | All functions and errors in this module are assigned to the <code><nowiki>http://basex.org/modules/csv</nowiki></code> namespace, which is statically bound to the {{Code|csv}} prefix.<br/> | ||
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===XQuery=== | ===XQuery=== | ||
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With the {{Code|xquery}} format, CSV records are converted to a sequence of arrays: | With the {{Code|xquery}} format, CSV records are converted to a sequence of arrays: | ||
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* With {{Code|attributes}} conversion, field names are stored in {{Code|name}} attributes | * With {{Code|attributes}} conversion, field names are stored in {{Code|name}} attributes | ||
* With {{Code|xquery}} conversion, the input is converted to an XQuery map | * With {{Code|xquery}} conversion, the input is converted to an XQuery map | ||
− | | {{Code|direct}}, {{Code|attributes}}, {{Code| | + | | {{Code|direct}}, {{Code|attributes}}, {{Code|xquery}} |
| {{Code|direct}} | | {{Code|direct}} | ||
| | | | ||
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|- | |- | ||
| width='120' | '''Signatures''' | | width='120' | '''Signatures''' | ||
− | |{{Func|csv:parse|$ | + | |{{Func|csv:parse|$string as xs:string?|item()?}}<br/>{{Func|csv:parse|$string as xs:string?, $options as map(*)?|item()?}} |
|- | |- | ||
| '''Summary''' | | '''Summary''' | ||
− | |Converts the CSV | + | |Converts the CSV {{Code|$string}} to an XQuery value. The {{Code|$options}} argument can be used to control the way the input is converted. |
|- | |- | ||
| '''Errors''' | | '''Errors''' | ||
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|- | |- | ||
| width='120' | '''Signatures''' | | width='120' | '''Signatures''' | ||
− | |{{Func|csv:serialize|$input as | + | |{{Func|csv:serialize|$input as item()?|xs:string}}<br/>{{Func|csv:serialize|$input as item()?, $options as map(*)?|xs:string}} |
|- | |- | ||
| '''Summary''' | | '''Summary''' | ||
− | |Serializes the | + | |Serializes the specified {{Code|$input}} as CSV, using the specified {{Code|$options}}, and returns the result as string. |
+ | Values can also be serialized as CSV with the standard [[Serialization]] feature of XQuery: | ||
+ | * The parameter {{Code|method}} needs to be set to {{Code|csv}}, and | ||
+ | * the options presented in this article need to be assigned to the {{Code|csv}} parameter. | ||
|- | |- | ||
| '''Errors''' | | '''Errors''' | ||
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let $records := $csv('records') | let $records := $csv('records') | ||
for $name at $pos in $csv('names')?* | for $name at $pos in $csv('names')?* | ||
− | let $values := $records($pos) | + | let $values := $records?($pos) |
return ( | return ( | ||
'* ' || $name || ': ' || string-join(distinct-values($values), ', ') | '* ' || $name || ': ' || string-join(distinct-values($values), ', ') | ||
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=Errors= | =Errors= | ||
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− | |||
{| class="wikitable" width="100%" | {| class="wikitable" width="100%" | ||
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=Changelog= | =Changelog= | ||
+ | |||
+ | ; Version 9.1 | ||
+ | * Updated: [[#csv:parse|csv:parse]] can be called with empty sequence. | ||
;Version 9.0 | ;Version 9.0 | ||
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* Added: {{Code|xquery}} option | * Added: {{Code|xquery}} option | ||
* Removed: {{Code|map}} option | * Removed: {{Code|map}} option | ||
− | * Updated: error codes | + | * Updated: error codes updated; errors now use the module namespace |
;Version 8.6 | ;Version 8.6 |
Revision as of 14:40, 16 April 2019
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.
Contents
Conventions
All functions and errors in this module are assigned to the http://basex.org/modules/csv
namespace, which is statically bound to the csv
prefix.
Conversion
XML: Direct, Attributes
If the direct
or attributes
format is chosen, a CSV string is converted to XML:
- 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 totrue
, 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 tofalse
, 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.
- Empty names are represented by a single underscore (
- If
format
is set toattributes
, 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
With the xquery
format, CSV records are converted to a sequence of arrays:
- The resulting value will be a map with a
records
and an optionalnames
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 totrue
.
The CSV map 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 enumerated strings for all records:
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.
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:
|
direct , attributes , xquery
|
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:
|
yes , no
|
yes
|
yes
|
backslashes
|
Specifies how quotes and other characters are escaped:
|
yes , no
|
no
|
no
|
Functions
csv:parse
Signatures | csv:parse($string as xs:string?) as item()? csv:parse($string as xs:string?, $options as map(*)?) as item()?
|
Summary | Converts the CSV $string to an XQuery value. The $options argument can be used to control the way the input is converted.
|
Errors | parse : the input cannot be parsed.
|
csv:serialize
Signatures | csv:serialize($input as item()?) as xs:string csv:serialize($input as item()?, $options as map(*)?) as xs:string
|
Summary | Serializes the specified $input as CSV, using the specified $options , and returns the result as string.
Values can also be serialized as CSV with the standard Serialization feature of XQuery:
|
Errors | serialize : 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 $csv := csv:parse($text, $options) return ( 'Distinct values:', let $records := $csv('records') for $name at $pos in $csv('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 |
---|---|
parse
|
The input cannot be parsed. |
serialize
|
The node cannot be serialized. |
Changelog
- Version 9.1
- Updated: csv:parse can be called with empty sequence.
- Version 9.0
- Added:
xquery
option - Removed:
map
option - Updated: error codes updated; errors now use the module namespace
- 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 tomap
. - Added:
format
andlax
options
The module was introduced with Version 7.7.2.