Design

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subsequence

The subsequence function in XQuery is designed to retrieve a specific portion of a sequence based on a starting location and an optional length. It allows extracting parts of a sequence efficiently, focusing only on the desired segment.

Syntax

fn:subsequence(sourceSeq, startingLoc, length)

The following table describes the argument for this command:

Argument	Required/Optional	Description
sourceSeq	Required	The input sequence from which a subsequence will be extracted.
startingLoc	Optional	The 1-based position within $sourceSeq where the subsequence starts. Non-integer values are rounded to the nearest integer. If $startingLoc is less than 1, it adjusts appropriately to start from the beginning of the sequence.
length	Optional	The number of items to include in the subsequence. Non-integer values are rounded to the nearest integer. If not specified or if the value is such that the subsequence extends beyond the end of $sourceSeq , all remaining items are included.

Return Value

Returns the contiguous sequence of items in the value of

$sourceSeq

beginning at the position indicated by the value of

$startingLoc

and continuing for the number of items indicated by the value of

$length

$startingLoc

is beyond the end of the sequence or

$length

is 0 or negative, it returns an empty sequence.

Examples

The following table lists some sample values and return values:

SAMPLE FUNCTION	OUTPUT
fn:subsequence( ('a', 'b', 'c', 'd', 'e'), 3)	('c', 'd', 'e')
fn:subsequence( ('a', 'b', 'c', 'd', 'e'), 3, 2)	('c', 'd')
fn:subsequence( ('a', 'b', 'c', 'd', 'e'), 3, 10)	('c', 'd', 'e')
fn:subsequence( ('a', 'b', 'c', 'd', 'e'), 10)	()
fn:subsequence( ('a', 'b', 'c', 'd', 'e'), -2, 5)	('a', 'b')
fn:subsequence( (), 3)	()
fn:subsequence((5, 10, 15, 20), 2.5, 2.6)	15, 20