MarkLogic 9 Product Documentation

fn:subsequence

fn:subsequence(
   $sourceSeq as item()*,
   $startingLoc as xs:double,
   [$length as xs:double]
) as item()*

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 functionFS.

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.

Example

Assume $seq = ($item1, $item2, $item3, $item4, ...)

fn:subsequence($seq, 4) returns ($item4, ...)

fn:subsequence($seq, 3, 2) returns ($item3, $item4)