two dimensional arrays

dmjcunha

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May 29, 2011, 6:35:41 PM5/29/11

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Hi. I don't know much of postscript I would like some help. How can I
create a 2 dimensional array of null elements? How can I put an
element in a 2 dimensional array? And how can I get an element in a 2
dimensional array?
Thank's in advance.

dmjcunha

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May 29, 2011, 6:37:00 PM5/29/11

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Thanks in advance.

Mark T. B. Carroll

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May 29, 2011, 6:48:33 PM5/29/11

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dmjcunha <dmjc...@gmail.com> writes:

You do it as an array of one-dimensional arrays. One useful trick can
be, if an element can't take many different values, an array of strings
can work too.

Mark

luser- -droog

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May 29, 2011, 10:57:08 PM5/29/11

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As Mark said, postscript doesn't have multi-dimensional arrays per
se.
But since an array is a first-class object, arrays can contain arrays
to an arbitrary depth.

Probably the easiest way to create an n-element array of m-element
arrays of null is:

[ n { m array } repeat ]

So if you define A to yield a 2 by 2 array,

/A [ 2 { 2 array } repeat ] def

you can set element (x,y) by getting row x and putting into column y.

A 0 get 0 1 put
A 0 get 1 0 put
A 1 get 0 0 put
A 1 get 1 1 put

This would be equivalent to constructing the array more directly:

/A [ [ 1 0 ] [ 0 1 ] ] def

For retrieving element (0,0) you can do:

A 0 get 0 get

Or the "shortcut":

A [ 0 0 ] { get } forall

HTH
L
X
T

luser- -droog

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May 30, 2011, 12:29:27 AM5/30/11

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I was intrigued enough to explore whether the "shortcut" could be
used for both put and get. The result is a little complicated, but
it works.

%!

% array {all-but} {last} forall-1 -
% "forall minus one"
% execute {all-but} for elements 0 .. n-2
% execute {last} for element n-1
/STATIC 2 array def
/forall-1 {
<<
0 { pop pop pop } % length == 0: do nothing
1 { exch pop forall } % length == 1: do {last}
>>
3 index length %dup =
2 copy known { get exec }{ pop pop
2 index 0
1 index length
1 sub getinterval %dup ==
3 1 roll
4 -1 roll
dup length 1 sub get %dup =
exch
//STATIC astore pop
forall
//STATIC aload pop
exec
} ifelse
} def

% m-array [ indices ] mget element(indices)
/mget {
{ get } forall
} def

% m-array [ indices ] value mput -
/mput {
3 1 roll { get } { 3 -1 roll put } forall-1
} def

/A
[ 5 {
[ 5 {
[ 5 { null } repeat ]
} repeat ]
} repeat ] def

A [ 4 4 4 ] 37 mput
A [ 4 4 4 ] mget
=

currentfile flushfile
!!gs %
GPL Ghostscript 8.62 (2008-02-29)
Copyright (C) 2008 Artifex Software, Inc. All rights reserved.
This software comes with NO WARRANTY: see the file PUBLIC for details.
37
GS>GS>

dmjcunha

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May 30, 2011, 8:05:31 AM5/30/11

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Thank you very much for the very helpful answers.

luser- -droog

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May 31, 2011, 1:43:45 AM5/31/11

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On May 29, 5:48 pm, "Mark T. B. Carroll" <m...@bcs.org> wrote:

One advantage of postscript polymorphism is that all composite
objects
can be accessed using the same syntax with get and put.

/A [ [ 16#30 16#31 16#32 16#33 ]
[ 16#34 16#35 16#36 16#37 ] ] def
/B [ (0123) (4567) ] def
/C << 0 (0123) 1 (4567) >> def

A [ 0 0 ] {get} forall

B [ 0 0 ] {get} forall
C [ 0 0 ] {get} forall

All three of these fetch the integer 48 (ascii zero) using 0 get 0
get.
But one is an array of arrays of integers, one is an array of strings,
and the third is a dictionary of strings with integer keys.

Gernot Hoffmann

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Jun 4, 2011, 4:43:33 AM6/4/11

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As an alternative to the concept 'Arrays in Array':
Use strictly onedimensional arrays and memory mapping functions.

Here comes Matrix-Library (Linear Algebra etc.)

Description in chapter 18:

http://www.fho-emden.de/~hoffmann/pstutor22112002.pdf

Source code (executable), rename *.txt as *.eps:

http://www.fho-emden.de/~hoffmann/matrixlib.txt

The programming style is very basic and therefore understandable.
Lacking speed is no issue for my applications.

Best regards --Gernot Hoffmann