Difference between revisions of "CSV Module"
(→XQuery) |
(→XQuery) |
||
Line 37: | Line 37: | ||
* <code>$csv?records(2)</code> returns all entries of the 2nd field (column) | * <code>$csv?records(2)</code> returns all entries of the 2nd field (column) | ||
* <code>$csv?names?*</code> returns the names of all fields (if available) | * <code>$csv?names?*</code> returns the names of all fields (if available) | ||
− | * Return enumerated | + | * Return enumerated string for each record: |
<pre class="brush:xquery"> | <pre class="brush:xquery"> | ||
for $record at $pos in $csv?records | for $record at $pos in $csv?records |
Revision as of 17:56, 26 October 2017
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 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 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
CSV records can be converted to a plain 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 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 enumerated string 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:
|
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:
|
yes , no
|
yes
|
yes
|
backslashes
|
Specifies how quotes and other characters are escaped:
|
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 tomap
. - Added:
format
andlax
options
The module was introduced with Version 7.7.2.