[fo] array:index-where

[michaelhkay]

There is a need for an array:index-where() function to operate on arrays in the same way as fn:index-where() operates on sequences/

Use case: consider XMark query Q4, which uses the << operator:

(: Q4. List the reserves of those open auctions where a
       certain person issued a bid before another person. :)

for    $b in /site/open_auctions/open_auction
where  $b/bidder/personref[@person="person18829"] <<
            $b/bidder/personref[@person="person10487"]
return <history>{ $b/reserve }</history>

With the bidders held in an array like this:

     "bidders": [
        { "increase":18, "time":"13:16:15", "date":"2001-06-13", "personref":"person0" },
        { "increase":12, "time":"11:29:44", "date":"2000-09-18", "personref":"person23" },
        { "increase":18, "time":"10:23:59", "date":"1998-01-07", "personref":"person14" },
        { "increase":4.5, "time":"14:00:39", "date":"2001-07-10", "personref":"person16" }
      ],

the best way of expressing this query seems to be:

for    $b in ?open_auctions?*
let    $bidders := $b?bidders
where  array:index-where($bidders, ->($bidder) {$bidder?personref="person18829"}) <
            array:index-where($bidders, ->($bidder) {$bidder?personref="person10487"})
return <history>{ $b?reserve }</history>

[dnovatchev]

The currently provided oracle implementation in the spec is written in XQuery :

for $item at $position in $input where $predicate($item) return $position

and is more complex than the following pure XPath 3.1 implementation:

index-of($seq ! $pred(.), true())

Besides being simpler, the Xpath expression above can be directly used in both XSLT and XQuery, without needing any changes/adaptation.

@michaelhkay Could we use the above pure XPath 3.0 definition/implementation of the semantics of this function?

[michaelhkay]

Sure, no problems.

[dnovatchev]

index-of($seq ! $pred(.), true())

Sorry, I thought this was the fn:index-where, and for that the above expression works.

One XPath oracle function for array:index-where is:

index-of(array:members($array) ! $pred(.), true())

[ndw]

Closed by #258.