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
--
Devon McCormick, CFA
^me^ at acm.
org is my
preferred e-mail
----------------------------------------------------------------------
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