stencil : size of window

[Yves]

Dear All,

with

      {⊂⍵} ⌺ 2 ⊢ 'mississippi'
┌→──────────────────────────────────────────────────┐
│ ┌→─┐ ┌→─┐ ┌→─┐ ┌→─┐ ┌→─┐ ┌→─┐ ┌→─┐ ┌→─┐ ┌→─┐ ┌→─┐ │
│ │mi│ │is│ │ss│ │si│ │is│ │ss│ │si│ │ip│ │pp│ │pi│ │
│ └──┘ └──┘ └──┘ └──┘ └──┘ └──┘ └──┘ └──┘ └──┘ └──┘ │
└∊──────────────────────────────────────────────────┘

result is exactly what we expect.

but with

      {⊂⍵} ⌺ 3 ⊢ 'mississippi'
┌→──────────────────────────────────────────────────────────────────┐
│ ┌→──┐ ┌→──┐ ┌→──┐ ┌→──┐ ┌→──┐ ┌→──┐ ┌→──┐ ┌→──┐ ┌→──┐ ┌→──┐ ┌→──┐ │
│ │ mi│ │mis│ │iss│ │ssi│ │sis│ │iss│ │ssi│ │sip│ │ipp│ │ppi│ │pi │ │
│ └───┘ └───┘ └───┘ └───┘ └───┘ └───┘ └───┘ └───┘ └───┘ └───┘ └───┘ │
└∊──────────────────────────────────────────────────────────────────┘

i need to correct by

      1↓ ¯1↓ {⊂⍵} ⌺ 3 ⊢ 'mississippi'
┌→──────────────────────────────────────────────────────┐
│ ┌→──┐ ┌→──┐ ┌→──┐ ┌→──┐ ┌→──┐ ┌→──┐ ┌→──┐ ┌→──┐ ┌→──┐ │
│ │mis│ │iss│ │ssi│ │sis│ │iss│ │ssi│ │sip│ │ipp│ │ppi│ │
│ └───┘ └───┘ └───┘ └───┘ └───┘ └───┘ └───┘ └───┘ └───┘ │
└∊──────────────────────────────────────────────────────┘

Everything gets worse when i change 'mississippi' to ' mississippi '.
i dont search same information with one or other.

one more good with

      {⊂⍵} ⌺ 2 ⊢ ' mississippi '
┌→────────────────────────────────────────────────────────────┐
│ ┌→─┐ ┌→─┐ ┌→─┐ ┌→─┐ ┌→─┐ ┌→─┐ ┌→─┐ ┌→─┐ ┌→─┐ ┌→─┐ ┌→─┐ ┌→─┐ │
│ │ m│ │mi│ │is│ │ss│ │si│ │is│ │ss│ │si│ │ip│ │pp│ │pi│ │i │ │
│ └──┘ └──┘ └──┘ └──┘ └──┘ └──┘ └──┘ └──┘ └──┘ └──┘ └──┘ └──┘ │
└∊────────────────────────────────────────────────────────────┘

and desastrous with

      {⊂⍵} ⌺ 3 ⊢ ' mississippi '
┌→──────────────────────────────────────────────────────────────────────────────┐
│ ┌→──┐ ┌→──┐ ┌→──┐ ┌→──┐ ┌→──┐ ┌→──┐ ┌→──┐ ┌→──┐ ┌→──┐ ┌→──┐ ┌→──┐ ┌→──┐ ┌→──┐ │
│ │  m│ │ mi│ │mis│ │iss│ │ssi│ │sis│ │iss│ │ssi│ │sip│ │ipp│ │ppi│ │pi │ │i  │ │
│ └───┘ └───┘ └───┘ └───┘ └───┘ └───┘ └───┘ └───┘ └───┘ └───┘ └───┘ └───┘ └───┘ │
└∊──────────────────────────────────────────────────────────────────────────────┘

i hope for another time to choose if i accept (or not) to add information to center window over string vector or image matrix.

Regards,
Yves

[Veli-Matti]

Hi,
afaik, the stencil operator has been designed to work just out of the border as in your examples (see e.g. Roger's blog). If you need only the vector subsets of a certain length, the n-wise reduction would be what you need:

      3,/'mississippi'
┌───┬───┬───┬───┬───┬───┬───┬───┬───┐
│mis│iss│ssi│sis│iss│ssi│sip│ipp│ppi│
└───┴───┴───┴───┴───┴───┴───┴───┴───┘

-Veli-Matti

[Yves]

Great thanks Veli-Matti ! i don't know this possibility of "n-wise". now, i use it.

With your comment

the stencil operator has been designed to work just out of the border

first, stencil operator is build to optimize browse of a structure AND apply a transformation ON each spot.

second, window is only "how you see univers".
actually, you're right, window's stencil work out of the border. for some application of filter to picture, you'll need "a short local apply" without alteration on "global part". example, at the TV, you blur only head of people, not all of images.

third point wellknow about a different universe is like game of life.
you work out of the border, but you fill with the other side of your structure.

at this time, i know only these 3 windows. i don't exclude other possibilty, may be as unusual as strange.

Yves