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>