Re: Data Arrays

A multidimensional array is not hard to use from a two dimensional array.  
Looking
at the way arrays are stored you can very easily build a function to use a 2 
dimensional
array as a 3 dimentional array.  (Er, maybe I mean 1 and 2 dimensional, now I'm 
getting
confused).

Say, for instance, I have an array set up as

D abc    DS          100
D  abc1                   10A

if I want to look at this as a 10 x 10 array the math is easy.

to get any element, such as 2 x 3 you just multiply X-1 * 10 + Y

2 - 1 * 10 = 10 + 3 = 13.  So, element [2, 3] = [13]

I could see building a function to return this but it would require
4 parameters, size of array X, size of array Y, occurrence X and occurance Y.
This would return a single number, the element number in the 2 dimensional 
array.

D         Eval    Return = (OccurX - 1) * ArrayX + OccurY

Turn this into a % function and you could do stuff like:

D         Eval   MyArray[%ConvertArray(10, 10, 2, 3)] = someval

Admittedly, this is not as easy as calling MyArray[2, 3] directly.

Regards,

Jim Langston

Peter Dow wrote:
> 
> Hi James,
> 
> Let's see if I can come up with an example code.
> 
>     D abc        DS        10 (occurrences that is)
>     D  abc1                    10A
> 
>     D xyz        DS                based(ptrXYZ)
>     D  xyz1                    10A
> 
>     c     1        occur    abc
>     c              eval     ptrXYZ = %addr(abc)
>     c     2        occur    abc
> 
>     c              if        abc1 = xyz1 (this is comparing 2 different
> occurrences)
>     c                ...
>     c              endif
> 
> As I said, I haven't actually tried this, but my understanding is that after
> the 2nd OCCUR stmt, the xyz data structure is still pointing to the 1st
> occurrence. The %addr(abc) returns a pointer to whatever the current
> occurrence is.
> 
> As to using pointers to do multi-dimensional arrays, I think you're right it
> might get pretty ugly. IBM almost slipped up and gave it to us with those
> array subfields, where you can overlay an array with subfields of an array
> element and then sort the array by those subfields. But they didn't allow
> the subfields to be arrays.
> 
> I haven't had much need for multi-dimensional arrays, but the couple of
> times I have, they've been just 2-D arrays, which are fairly easily
> simulated by calculations or an array within a multi-dimensional data
> structure.
> 
> HTH
> Peter Dow
> Dow Software Services, Inc.
> 909 425-0194 voice
> 909 425-0196 fax
+---
| This is the RPG/400 Mailing List!
| To submit a new message, send your mail to RPG400-L@midrange.com.
| To subscribe to this list send email to RPG400-L-SUB@midrange.com.
| To unsubscribe from this list send email to RPG400-L-UNSUB@midrange.com.
| Questions should be directed to the list owner/operator: david@midrange.com
+---