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MarkLogic Server 11.0 Product Documentation
fn.subsequence

fn.subsequence(
   sourceSeq as Sequence,
   startingLoc as Number,
   [length as Number]
) as Sequence

Summary

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.

As described in https://www.w3.org/TR/xpath-functions/:

In the two-argument case, fn.subsequence returns a sequence comprising those items of $sourceSeq whose index position (counting from one) is greater than or equal to the value of $startingLoc (rounded to an integer):

$sourceSeq[fn:round($startingLoc) le $p]

No error occurs if $startingLoc is zero or negative.

In the three-argument case, The function returns a sequence comprising those items of $sourceSeq whose index position (counting from one) is greater than or equal to the value of $startingLoc (rounded to an integer), and less than the sum of $startingLoc and $length (both rounded to integers):

$sourceSeq[fn:round($startingLoc) le $p and $p lt fn:round($startingLoc) + fn:round($length)]

No error occurs if $startingLoc is zero or negative, or if $startingLoc plus $length exceeds the number of items in the sequence, or if $length is negative.

Notes:

If $sourceSeq is the empty sequence, the empty sequence is returned.

If $startingLoc is zero or negative, the subsequence includes items from the beginning of the $sourceSeq.

If $length is not specified, the subsequence includes items to the end of $sourceSeq.

If $length is greater than the number of items in the value of $sourceSeq following $startingLoc, the subsequence includes items to the end of $sourceSeq.

The first item of a sequence is located at position 1, not position 0.

For detailed type semantics, see Section 7.2.13 The fn:subsequence functional specification.

The reason the function accepts arguments of type xs:double is that many computations on untyped data return an xs:double result; and the reason for the rounding rules is to compensate for any imprecision in these floating-point computations.

Parameters
sourceSeq A Sequence of items from which a subsequence will be selected. If you pass in a single value, it is treated as a Sequence with that single item; therefore, if you pass in an array, fn.subsequence will treat the array as a single-item sequence. If you mean to get the subsequence of each item in the array, then you can call xdmp.arrayValues on the array.
startingLoc The starting position of the start of the subsequence.
length The length of the subsequence.

Example

const seq = xdmp.arrayValues(["item1", "item", "item3", "item4" , "..."]);
fn.subsequence(seq, 4)
=> (item4, ...)

const seq = xdmp.arrayValues(["item1", "item", "item3", "item4" , "..."]);
fn.subsequence(seq, 3, 2)
=> (item3, item4)

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