Tcl Source Code

  %lsearch -stride 3 -index 0 -subindices -inline {a1 b1 c1 a2 b2 c2} a*
  a1

  %lsearch -stride 3 -index 0 -subindices -inline -all {a1 b1 c1 a2 b2 c2} a*
  a1 b1 c1 a2 b2 c2

If we omit the -inline flag the indices are as expected

  %lsearch -stride 3 -index 0 -subindices -all {a1 b1 cc1 a2 b2 c2} a*
  0 3

This second result is unexpected. (and gives the same result as with -subindices omitted)

Tip 351 example 5 indicates some level of consistency with the nested equivalent should be expected.

  %lsearch -index 0 -subindices -inline {{a1 b1 c1} {a2 b2 c2}} a*
  a1

  %lsearch -index 0 -subindices -inline -all {{a1 b1 c1} {a2 b2 c2}} a*
  a1 a2

The second result here is what I would have expected for the stridden version.

This makes certain operations with flattened lists harder to do. It can be worked around by using combinations of lseq, lmap etc instead of lsearch - but nothing seems as performant as a single lsearch -stride operation.

See my example code in bug https://core.tcl-lang.org/tcl/tktview/edebb6a4 regarding empty strings.
In that case - I had to artificially use an extra level of indices to extract what's required - and then ran headlong into that issue regarding empty string members (and also wrong results for members containing spaces)

One workaround I've used is to list protect every member of my flattened list - and then use the double index such as -index {0 0}
The additional prep overhead of doing something like: lmap v $list {list v} on a large list wipes out any performance gains from using lsearch -stride.

Merged by commit [57bafdc65d]. Thanks for the bug report, fix, test and review. Harald

So -inline -subindices is a search-and-extract operation. That makes sense. I've built and reviewed [ab992d35ac], and I think it's ready to be merged to trunk.

Tests are now in with checkin [ab992d35ac].

IMHO, the patch looks good now.

Anybody may review ?

Remark, that this does not concern TCL 8.6, as "-stride" is not present.

Thanks for all, Harald

Thanks for trying this out Harald.
I propose the following tests:

  test lsearch-27.7 {lsearch -stride + -subindices option single index} {
      lsearch -inline -stride 3 -subindices -all -index 1  {{x a} {y b} {x c} {xx a} {xx b} {xx c} {xxx a} {y b} {xxx c}} {y b}
  } {{y b} {y b}}
  test lsearch-27.8 {lsearch -stride + -subindices option single index} {
      lsearch -inline -stride 3 -subindices -all -index end {{x a} {y b} {xc} {xx a} {xx b} {xx c} {xxx a} {y b} {}} *
  } {xc {xx c} {}}

Julian, thank you for the patch. It is now with checkin [7274285f90] in branch [5a1aaa20-lsearch-stride], derived from main (tcl 9).

I tried your examples: Tcl 9.0.0:

% lsearch -stride 3 -index 0 -subindices -inline {a1 b1 c1 a2 b2 c2} a*
a1
% lsearch -stride 3 -index 0 -subindices -inline -all {a1 b1 c1 a2 b2 c2} a*
a1 b1 c1 a2 b2 c2
% lsearch -stride 3 -index 0 -subindices -all {a1 b1 c1 a2 b2 c2} a*
0 3

Branch [5a1aaa20-lsearch-stride]:

% lsearch -stride 3 -index 0 -subindices -inline {a1 b1 c1 a2 b2 c2} a*
a1
% lsearch -stride 3 -index 0 -subindices -inline -all {a1 b1 c1 a2 b2 c2} a*
a1 a2
% lsearch -stride 3 -index 0 -subindices -all {a1 b1 c1 a2 b2 c2} a*
0 3

This looks great and as the expected behavior.

Would you mind to author a test case?

Thank you and take care, Harald

Notes for attached patch:

patch for -stride -index -all -inline -subindices 

Only affects the case where there is a single element in -index 

#before 
  lsearch -stride 2 -index end -all -subindices -inline {a {sub a} b {sub b} c {etc c}} sub*
    a {sub a} b {sub b}

#after
  lsearch -stride 2 -index end -all -subindices -inline {a {sub a} b {sub b} c {etc c}} sub*
  {sub a} {sub b}

Aside from consistency with the nested equivalent, it's not self-consistent.

Another way of looking at this is that -all should always be equivalent to building the list by iterating using -start.

  lsearch -start 0 -stride 2  -index 1  -inline -subindices {abc abc abc bcd abc cde abc def} *c*
    abc

  lsearch -start 2 -stride 2  -index 1  -inline -subindices {abc abc abc bcd abc cde abc def} *c*
    bcd

  lsearch -start 4 -stride 2  -index 1  -inline -subindices {abc abc abc bcd abc cde abc def} *c*
    cde

  lsearch -all -start 0 -stride 2  -index 1  -inline -subindices {abc abc abc bcd abc cde abc def} *c*
    abc abc abc bcd abc cde

This should be: abc bcd cde
but it's returning each matched stride-group instead.

This result is already obtainable by omitting -subindices

  lsearch -all -start 0 -stride 2  -index 1  -inline {abc abc abc bcd abc cde abc def} *c*
    abc abc abc bcd abc cde


I'm not aware of any case other than with a single -index combined with -stride, -subindices -all where this inconsistency occurs.

There aren't many documented examples for -stride, and no test coverage for this specific case.
It took me a while to understand there was an inconsistency, and although the -stride option has been available for a while - I think with the release of Tcl 9 this should be high on the priority list.