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Richard · Guest

I would like to iterate over a sub-dimension of a multidimensional
dynamic array.

The compiler complains about incompatible types.
------------------
type
Ttwod = array of array of longword;

procedure foo (twod:Ttwod);
var
oned: array of longword;
i, j, sum, floormean : longword;
begin
for i := low(twod) to high(twod) do begin
oned := twod[i];
for j := low(oned) to high(oned) do begin
// do stuff
Inc (sum, oned[j]);
end;
floormean := sum div j;
end;
end;
------------------

In this case I would sum one[j] in the hopes that it compiles to code
that is more efficient than if it were summing twod[i,j].

The presumption is that there would be fewer array address calculations
going on 'behind the scenes' when using [j] instead [i,j]

alanglloyd@aol.com · Guest

The array of longword in TTWod is not the same type as the array of
longword declared for oned.

For example declared variables ..

A : array of longword;
B : array of longword;

.... are of two different types. Read the Delphi Object Pascal Language
Guide.

If you want to do what you appear to want, you must declare ...

TOneWord = array of longword;

TTwoWord = array of TOneWord;

Oned : TOneWord;

..... then it would compile.

I doubt if you would see any difference in speed from using ...

Sum := 0;
for i := Low(TwoD) to High(TwoD) do
for j := Low(TwoD[1]) to High(TwoD[1]) do
inc(Sum, TwoD[i, j]);

.... maybe its even slightly faster <g>.

You have also forgotten to initialise Sum.

Alan Lloyd