Re: [basex-talk] Weird behaviour with sequence and random:integer

[Marco Lettere]

Everytime one learns something new.

Thanks for the explanation!

M.

On 22/05/24 15:41, Christian Grün wrote:

Hi Marco,

> ("a", "b", "c")[trace(1 + random:integer(3))]

The filter expression is defined in such a way that the predicate is evaluated anew for every item of the sequence. If you want random:integer(3) to be evaluated only once, you can either bind it to a variable…

let $r := random:integer(3) + 1
return ("a", "b", "c")]$r]

…or use functions like fn:subsequence:

subsequence(("a", "b", "c"), random:integer(3) + 1, 1)

Hope this helps,
Christian



Marco Lettere <m.lett...@gmail.com> schrieb am Mi., 22. Mai 2024, 15:34:

    Dear all,

    I have this strange behavior when running in BaseX 10.4:

    ["a","b","c"](1 + random:integer(3))

    I got something empty result, sometimes (correctly) one out of the
    three, sometimes two results...

    I report the results and the trace in [1] and [2].

    What is the reason for this?

    Thank you.

    Marco.

    [1] Two results
    a
    c

    Evaluating:
    1
    3
    3
    Compiling:
    - rewrite list to xs:string sequence: ("a", "b", "c")
    - swap operands: (1 + random:integer(3))
    Optimized Query:
    ("a", "b", "c")[trace((random:integer(3) + 1))]
    Query:
    ("a", "b", "c")[trace(1 + random:integer(3))]
    Result:
    - Hit(s): 2 Items
    - Updated: 0 Items
    - Printed: 3 b
    - Read Locking: (none)
    - Write Locking: (none)
    Timing:
    - Parsing: 0.21 ms
    - Compiling: 0.4 ms
    - Optimizing: 0.1 ms
    - Evaluating: 0.57 ms
    - Printing: 0.02 ms
    - Total Time: 1.31 ms


    [2] Empty result
    ()

    Evaluating:
    3
    3
    1
    Compiling:
    - rewrite list to xs:string sequence: ("a", "b", "c")
    - swap operands: (1 + random:integer(3))
    Optimized Query:
    ("a", "b", "c")[trace((random:integer(3) + 1))]
    Query:
    ("a", "b", "c")[trace(1 + random:integer(3))]
    Result:
    - Hit(s): 0 Items
    - Updated: 0 Items
    - Printed: 0 b
    - Read Locking: (none)
    - Write Locking: (none)
    Timing:
    - Parsing: 0.16 ms
    - Compiling: 0.41 ms
    - Optimizing: 0.15 ms
    - Evaluating: 0.56 ms
    - Printing: 0.02 ms
    - Total Time: 1.3 ms
    Query Plan:
    <QueryPlan compiled="true" updating="false">
       <CachedFilter type="xs:string*">
         <StrSeq type="xs:string+" size="3">
           <Str type="xs:string" size="1">a</Str>
           <Str type="xs:string" size="1">b</Str>
           <Str type="xs:string" size="1">c</Str>
         </StrSeq>
         <FnTrace name="trace" type="xs:integer" size="1">
           <Arith op="+" type="xs:integer" size="1">
             <RandomInteger name="random:integer" type="xs:integer"
    size="1">
               <Int type="xs:integer" size="1">3</Int>
             </RandomInteger>
             <Int type="xs:integer" size="1">1</Int>
           </Arith>
         </FnTrace>
       </CachedFilter>
    </QueryPlan>