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

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.lettere@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>