It's not so much that it's of no use, but that it's redundant.

When your hook is a train where the first verb is a hook, you can
restructure either of them so that the other of those two hooks takes
over the responsibility of obtaining the hook's "left argument"
(presumably, this would eliminate the other hook).

I hope this helps,

-- 
Raul


On Sun, Feb 12, 2017 at 10:18 AM, R.E. Boss <[email protected]> wrote:
> I think the problem is that the big hook is of no use, that's what creates 
> confusion.
>
>    (data mp1 mn data)% # data
> 504 360 180
> 360 360   0
> 180   0 720
>
>    data mp1 mn data
> 2520 1800  900
> 1800 1800    0
>  900    0 3600
>
>    mp1 mn data
> 2520 1800  900
> 1800 1800    0
>  900    0 3600
>
>
> R.E. Boss
>
>
> -----Original Message-----
> From: Programming [mailto:[email protected]] On Behalf 
> Of 'Mike Day' via Programming
> Sent: zondag 12 februari 2017 12:02
> To: [email protected]
> Subject: Re: [Jprogramming] Hooked again
>
> It looks to me as if the two left hooks form one big left hook, not that I'm 
> into boxing:
>
>     mn =: -"1 mean
>     mp1=: mp~|:
>
>     ((mp1 mn)%#)data    NB. big "hook"
> 504 360 180
> 360 360   0
> 180   0 720
>
>     ((mp1 @: mn)%#)data   NB. mp1 after mn using @:
> 504 360 180
> 360 360   0
> 180   0 720
>
>     (([: mp1 mn)%#)data    NB. mp1 after mn using [:
> 504 360 180
> 360 360   0
> 180   0 720
>
> Any use?
>
> Mike
>
>
> On 12/02/2017 08:06, Lippu Esa wrote:
>> ]data=. 5 3 $ 90 60 90 90 90 30 60 60 60 60 60 90 30 30 30
>>
>> mean=: +/%#
>> mp=:  +/ . *
>> covmat=: ((mp~|:)(-"1 mean))%# NB. divede by n not n-1 to comply with
>> the example
>
>
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