I find it often convenient to use _ for missing or not found.
Maybe it should be better to use _. ?
2012/4/23 Henry Rich <henryhr...@nc.rr.com>
> That convenience would also obtain (in J) if the 'not found' result were
> _1; and then the 'not found' entry would be known in advance and we
> wouldn't have to calculate it.
>
> Henry Rich
>
> On 4/23/2012 5:28 PM, Devon McCormick wrote:
> > The convenience of index returning one more than the maximum is that
> > it allows you to put your null (or other default) value at the end of
> > your lookup vector, e.g.
> >
> > (Target,a:){~Source getIndex Target
> > +-+---+-++
> > |a|bcd|e||
> > +-+---+-++
> >
> > or maybe you want
> >
> > (Source,a:){~Source i. Target
> > +-+-+---++
> > |e|a|bcd||
> > +-+-+---++
> >
> > The last item is an empty vector because it's not found and that's the
> > extra item we put at the end.
> >
> > On Mon, Apr 23, 2012 at 7:35 AM, Henry Rich<henryhr...@nc.rr.com>
> wrote:
> >> Source =. 'a';'bcd';'e';'g'
> >> Target =. 'e';'a';'bcd';'f'
> >> getIndex =: i.~ NB. not e.
> >> shouldReturn =. 1 2 0 4 NB. 'not found' for i. is #x
> >> assert (Source getIndex Target)-:shouldReturn NB. -: not =
> >>
> >> Henry Rich
> >>
> >> On 4/23/2012 7:13 AM, Joe Bohart wrote:
> >>> Hi J'ers,
> >>>
> >>> I'm trying to write a verb that will
> >>> match the items in Source with Target
> >>> and return the index of items in Target
> >>> such that they are in the same order as
> >>> Source with nulls (or the J way of handling nulls)
> >>> if no match is found.
> >>>
> >>> This is what i have (and it's wrong):
> >>>
> >>> Source =. 'a';'bcd';'e';'g'
> >>> Target =. 'e';'a';'bcd';'f'
> >>> getIndex =: e.
> >>> shouldReturn =. 1 2 0 null
> >>> assert (Source getIndex Target)=shouldReturn
> >>>
> >>> In the forums I've found solution candidates,but
> >>> haven't been able to apply them and am a bit lost with:
> >>> I.@:E. and ;:
> >>>
> >>> The concept of expressing null or missing data in J I haven't
> >>> found much info on. Where can i find more information on nulls.
> >>>
> >>> Much Thanks -Joe
> >>> ----------------------------------------------------------------------
> >>> For information about J forums see http://www.jsoftware.com/forums.htm
> >>>
> >> ----------------------------------------------------------------------
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> >
> >
> >
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