Hi.
I am writing a program in Delphi and I need to use arrays.  My problem is that I will be running my program on
many different data sets, each with different sizes/numbers of particular variables.  What I am having to do
at the moment is declare my arrays at the beginning of my program such that it can handle any particular data
set that it encounters.

for example, I have to declare:

myArray = array[1..largestPossibleA, 1..largestPossibleB, 1..largestPossibleC] of integer;

This is making my arrays far to big however.  A lot of the time it is wasting space also, for example the
current data set might need a lot of the 1..largestPossibleA's but not many of the 1..largestPossibleB's and
C's (I hope I that last sentence makes sense :)   )

What I want is to be able to dynamically change/increase/decrease the size of the array as my program is
running (similar to what can be done in C++ I am told).  So for example I would read in my data and see that
the biggest A=10 and the biggest B = 15 and the biggest C = 10 for this data set, so I dynamically create an
array which is array[1..10, 1..15, 1..10] of integer/real/whatever.

I didnt think it was possible to do this in Pascal but someone told me that Delphi has something called
dynamic arrays.  I looked it up in the help but it was not very helpful at all.  Can someone help me with this
please???? (if you can help me it would be great if you were quite specific in your instructions as I am new
to Delphi)

Another thought I had to solve this problem was to:

a)read in the data
b)find out the ranges I need (ie the A and B and C etc..)
c)run a little program that read in my program and altered the constants A B and C (etc..) to be the size I
wanted and then
d)recompiled my program and ran it

Has someone written a unit that does this type of thing to help with array size problems??

all replies greatly appreciated

regards
andrew coyle

PS: please reply to mail (as well as news if you want) as my access to newsgroups is irregular :)

The memory requirements for a 10 x 15 x 10 array of number is not very
great.

==============================================

// Note:  the following looks indented properly with a fixed-width font

// Delphi 3 Example of 2-Dimensional Dynamic Array
CONST
    ArrayMaxCount = 65536;

TYPE
    pDoubleArray = ^TDoubleArray;
    TDoubleArray = ARRAY[0..ArrayMaxCount-1] OF DOUBLE;
    pMatrix = ^TMatrix;
    TMatrix = ARRAY[0..ArrayMaxCount-1] OF pDoubleArray;

procedure TForm1.Button1Click(Sender: TObject);
    CONST
        iCountMax = 500; // columns
        jCountMax = 1000; // rows
    VAR
        i : 0..iCountMax-1;
        j : 0..jCountMax-1;
        k : INTEGER;

        // Let's make Matrix 1000 rows of 500 columns =
        // 500,000 elements = 4,000,000 bytes
        Matrix: pMatrix;

        Sum : DOUBLE;
begin
    // Allocate the pointers to each row
    GetMem(Matrix, jCountMax*SizeOf(pMatrix));
    TRY

        // Allocate each row of DOUBLEs
        FOR j := 0 TO jCountMax-1 DO
            GetMem(Matrix[j], iCountMax*SizeOf(DOUBLE));

        TRY
            // Assign value to each Matrix element
            k := 1;
            FOR j := 0 TO jCountMax - 1 DO
            BEGIN
                FOR i := 0 TO iCountMax -1 DO
                BEGIN
                    Matrix[j]^[i] := k;
                    INC(k);
                END;
            END;

            // Add up all values in Matrix. The sum of 1..N = N*(N+1)/2, so
            // the sum should be (iCountMax*jCountMax)*(iCountMax*jCountMax
+ 1) / 2,
            // or in this case SUM(1..500,000) = 125,000,250,000.
            Sum := 0;
            FOR j := 0 TO jCountMax - 1 DO
                FOR i := 0 TO iCountMax -1 DO
                    Sum := Sum + Matrix[j]^[i];

            Button1.Caption := FloatToStr(Sum);

        FINALLY
            // Free each row of DOUBLEs
            FOR j := jCountMax-1 DOWNTO 0 DO
            FreeMem(Matrix[j]);

        END
    FINALLY
        // Free array of pointers
        FreeMem(Matrix)
    END
end;

Normally, I'd suggest that you also look at Items D-8 and D-10 in my Delphi
Math
FAQ and Links page.  (My web server is down right now, however.)

efg
_________________________________________
efg's Computer Lab:  http://infomaster.net/external/efg

Earl F. Glynn                 E-Mail:  EarlGl...@att.net
MedTech Research Corporation, Lenexa, KS  USA

On Thu, 02 Apr 1998 15:59:15 +1200, Sheryl Coyle

regards
A.G.

cc'd: yes

The answer is typecasting and dynamic memory allocating :

You get a pointer with the good size :

GetMem(MyP, MySize);
The Size should be calculated correctly, for example :
MySize:=20*5*20*SizeOf(Double);

Then you create the good type :
TMyArray = Array[0..0] of Double;

And if I need to get an element :
MyElem:=TMyArray(MyP^)[10,3,1];

Well, this is something like that. As my Delphi is out, I can't try this
now. It's like a jigsaw ;-)

Good luke, and ask me if more explanations are needed.

Regards,
--
Frdric GUILLIEN

Here is my Web site. Yet all in french (sorry, time missing...)
http://wwwperso.hol.fr/~fguillei

You might check out our Matrix Math Toolkit v 3 at our
website if you plan to do 'matrix' kinds of calcs...

--
Grace + Peace | Peter N Roth | Engineering Objects Int'l
         Now shipping version 4 of ClassBuilder++
Visit our website at http://www.inconresearch.com/eoi
"Random numbers are too important to be left to chance." - anon

type
  TMultiMatrix = class (TObject)
    constructor Create (dimensions: Integer);
    destructor Destroy; override;

    function GetX (index: array of Integer): Extended;
    procedure SetX (index: array of Integer; value: Extended);
  end;

You would use this class like this:

var
  m: TMultiMatrix;
  i, j, k: Integer;

begin
  m := TMultiMatrix.Create (3); // you need a 3-d matrix
  for i := 0 to 50 do // I assume zero-based indices
    for j := 0 to 12 do
      for k := 0 to 17 do
        m.SetX ([i, j, k], Extended (i + j + k) / 2);
//...
end;

The class is the tricky part :-) if you can't succeed in writing it (using
others' help) I will try to do it...

Mark

We have a Dynamic Array in our product but it simulates an XBASE array (very
dynamic access, mixed type elements and coordinates of either numeric or string
values) but its not as fast as the solution above for a strickly numeric array
(due to all the other stuff its doing) .  I've seen alot of interest in this
sort of thing though so who knows.

I know that a number of Matrix components are out there already if thats what
you really need.  If you do the component and have questions, I'll try to stay
tuned and try to help out.

Nate

 Foolproof systems always underestimate
 the ingenuity of a fool.

 Clipper Functions 3.0 for Delphi
 http://members.aol.com/clipfunc