For what it's worth, here's a parenthesis free implementation of my
two variant definitions of cross (and note that I am using what is
probably an unfamiliar J idiom here -- please feel free to ask for an
explanation, if I am not making sense):
selch=: #"0"1
orflp=: +.|.@
cross1=: ,@selch~ = orflp
cross2=: ,@selch~ =@i.@# orflp
Example use:
cross1 'abcde'
a e
b d
c
b d
a e
cross2 'abcde'
a e
b d
c
b d
a e
Here is a case where the implementation gives different results:
cross1 'abcba'
a c a
b b
a c a
cross2 'abcba'
a a
b b
c
b b
a a
FYI,
--
Raul
On Mon, Dec 10, 2012 at 2:48 PM, Raul Miller <rauldmil...@gmail.com> wrote:
> And, for what it's worth, here's a different plausible implementation
> of cross (different only for the case of duplicated letters in the
> argument when compared with the version I posted, below):
>
> (,@(#~"0"1) (+.|.)@=@(#\)) 'abcdedcba'
>
> Note that replacing = with =@(#\) should also work for Aai's original version.
>
> FYI,
>
> --
> Raul
>
> On Mon, Dec 10, 2012 at 1:28 PM, Raul Miller <rauldmil...@gmail.com> wrote:
>> Here's a version that works with duplicated values (except note that
>> there was no specification for what the behavior should be in this
>> case):
>>
>> (,@(#~"0"1) (+.|.)@=)'abcde'
>> a e
>> b d
>> c
>> b d
>> a e
>>
>> (,@(#~"0"1) (+.|.)@=)'abcdedcba'
>> a e a
>> b d d b
>> c c
>> b d d b
>> a e a
>>
>> --
>> Raul
>>
>> On Mon, Dec 10, 2012 at 1:21 PM, Roger Hui <rogerhui.can...@gmail.com> wrote:
>>> The expression fails if the argument has duplicate items. e.g.
>>>
>>> ((+.|.)@={"0 1 ' '&,.)'aabbb'
>>> |length error
>>> | ((+.|.)@={"0 1' '&,.)'aabbb'
>>>
>>>
>>>
>>> On Mon, Dec 10, 2012 at 10:18 AM, bob therriault
>>> <bobtherria...@mac.com>wrote:
>>>
>>>> That is lovely Arie,
>>>>
>>>> It is that kind of elegance that I was chasing with my rougher attempts.
>>>>
>>>> Using the (+.|.) hook simplifies (|.+.]) precisely and the {" 0 1
>>>> combined with ' '&,. means that the selection of the string becomes a
>>>> choice in each row of displaying either the corresponding element of the
>>>> string or a blank.
>>>>
>>>> Cheers, bob
>>>>
>>>> On 2012-12-10, at 1:11 AM, Aai wrote:
>>>>
>>>> > ((+.|.)@={"0 1 ' '&,.)'abcde'
>>>>
>>>> ----------------------------------------------------------------------
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>>>>
>>> ----------------------------------------------------------------------
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