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
>>>
>> ----------------------------------------------------------------------
>> For information about J forums see http://www.jsoftware.com/forums.htm
>
>
>
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