• "Saaa" <empty needmail.com> Jul 26 2008
• Rakan Alhneiti <rakan.alhneiti nospam.gmail.com> Jul 26 2008
• "Steven Schveighoffer" <schveiguy yahoo.com> Jul 26 2008
• "Steven Schveighoffer" <schveiguy yahoo.com> Jul 26 2008
• "Saaa" <empty needmail.com> Jul 27 2008
• "Steven Schveighoffer" <schveiguy yahoo.com> Jul 28 2008
• bearophile <bearophileHUGS lycos.com> Jul 28 2008
• "Jarrett Billingsley" <kb3ctd2 yahoo.com> Jul 28 2008
• bearophile <bearophileHUGS lycos.com> Jul 26 2008
• BCS <ao pathlink.com> Jul 27 2008

"Saaa" <empty needmail.com> writes:

Is there a easy way to set/read a multidimensional slice of an array?

I'd like to do something like this... :)

int array[][];
array.length=100;
array[].length=200; :  Error: slice expression array[] is not a modifiable 
lvalue

int array2[][];
array2.length=4;
array2[].length=2;
array2=[[1,2,3,4],[5,6,7,8]];

array[10..10+array2.length][150..150+array2[].length]=array2; 

Rakan Alhneiti <rakan.alhneiti nospam.gmail.com> writes:

Saaa wrote:
 Is there a easy way to set/read a multidimensional slice of an array?
 
 I'd like to do something like this... :)
 
 int array[][];
 array.length=100;
 array[].length=200; :  Error: slice expression array[] is not a modifiable 
 lvalue
 
 int array2[][];
 array2.length=4;
 array2[].length=2;
 array2=[[1,2,3,4],[5,6,7,8]];
 
 array[10..10+array2.length][150..150+array2[].length]=array2; 
 
 


Initialization of inner arrays in multidimensional arrays is done most 
of the type using loops
int array[][];
array.length = 100;
for(int i = 0;i<array.length;i++)
{
	array[i].length = 4;
}

as for slicing, i guess you will have to specify the starting and ending 
  index.
array2 = array1[0..5];

"Steven Schveighoffer" <schveiguy yahoo.com> writes:

"Rakan Alhneiti" wrote
 Saaa wrote:
 Is there a easy way to set/read a multidimensional slice of an array?

 I'd like to do something like this... :)

 int array[][];
 array.length=100;
 array[].length=200; :  Error: slice expression array[] is not a 
 modifiable lvalue

 int array2[][];
 array2.length=4;
 array2[].length=2;
 array2=[[1,2,3,4],[5,6,7,8]];

 array[10..10+array2.length][150..150+array2[].length]=array2;


 Initialization of inner arrays in multidimensional arrays is done most of 
 the type using loops
 int array[][];
 array.length = 100;
 for(int i = 0;i<array.length;i++)
 {
 array[i].length = 4;
 }


Probably done easiest with a foreach loop:

foreach(ref a; array)
    a.length = 4;

The slicing is somthing that would have to be done using loops.

you might not realize, but a multi-dimensional dynamic array is really an 
array of pointers, not one contiguous block of memory.  So each sub-array 
points to a different memory space, and could have different lengths.

a loop with foreach would look something like:

foreach(i, ref a; array[10..10+array2.length])
    a[] = array2[i];

Probably other ways to do it.

-Steve

"Steven Schveighoffer" <schveiguy yahoo.com> writes:

"Steven Schveighoffer" wrote
 "Rakan Alhneiti" wrote
 Saaa wrote:
 Is there a easy way to set/read a multidimensional slice of an array?

 I'd like to do something like this... :)

 int array[][];
 array.length=100;
 array[].length=200; :  Error: slice expression array[] is not a 
 modifiable lvalue

 int array2[][];
 array2.length=4;
 array2[].length=2;
 array2=[[1,2,3,4],[5,6,7,8]];

 array[10..10+array2.length][150..150+array2[].length]=array2;


 Initialization of inner arrays in multidimensional arrays is done most of 
 the type using loops
 int array[][];
 array.length = 100;
 for(int i = 0;i<array.length;i++)
 {
 array[i].length = 4;
 }


 Probably done easiest with a foreach loop:

 foreach(ref a; array)
    a.length = 4;

 The slicing is somthing that would have to be done using loops.

 you might not realize, but a multi-dimensional dynamic array is really an 
 array of pointers, not one contiguous block of memory.  So each sub-array 
 points to a different memory space, and could have different lengths.

 a loop with foreach would look something like:

 foreach(i, ref a; array[10..10+array2.length])
    a[] = array2[i];


err.. that should have been
a[150..150+array2[i].length] = array2[i];

-Steve 

"Saaa" <empty needmail.com> writes:

Thanks, the code now looks like this (and works :)

 int array[][];
 array.length=10;
 foreach(ref a; array)
  a.length = 5;

 int array2[][];
 array2.length=2;
 foreach(ref a; array)
  a.length = 6;

array2=[[1,2,3,4],[5,6,7,8]];

foreach(i, ref a; array[2..2+array2.length])
 a[1..1+array2[i].length] = array2[i];

 writefln(array2);
 writefln(array);

[[1,2,3,4],[5,6,7,8]]
[[0,0,0,0,0,0],[0,0,0,0,0,0],[0,1,2,3,4,0],[0,5,6,7,8,0],[0,0,0,0,0,0],
[0,0,0,0,0,0],[0,0,0,0,0,0],[0,0,0,0,0,0],[0,0,0,0,0,0],[0,0,0,0,0,0]]
--------------------------
//And for 3D:

 int array[][][];
 array.length=6;
 foreach(ref a; array)
 {
  a.length = 6;
  foreach(ref b; a)
   b.length = 6;
 }

 int array2[][][];
 array2.length=2;
 foreach(ref a; array2)
 {
  a.length = 2;
  foreach(ref b; a)
   b.length = 2;
 }


 array2=[[[1,2],[5,6]],[[9,9],[8,7]]];

 foreach(i, ref a; array[2..2+array2.length])
 foreach(ii, ref b; a[2..2+array2[0].length])
  b[1..1+array2[ii].length] = array2[i][ii];

 writefln(array2);
 writefln(array);
--------------------------
... erm I barely follow it myself :/

I think array can be static and maybe array2 will be as well and I'll 
manually keep the x,y and z sizes and do normal for-loops over them.

"Steven Schveighoffer" <schveiguy yahoo.com> writes:

"Saaa" wrote
 Thanks, the code now looks like this (and works :)

 int array[][];
 array.length=10;
 foreach(ref a; array)
  a.length = 5;

 int array2[][];


You can comment out these lines:

/*
 array2.length=2;
 foreach(ref a; array)
  a.length = 6;



 array2=[[1,2,3,4],[5,6,7,8]];


could be:

auto array2=[[1,2,3,4],[5,6,7,8]];

and get rid of the array2 declaration above.

At this point, you have thrown away all your work you did to set the lengths 
in array2 :)

Note that setting array2 this way just changes the array to point to the 
array literal, it doesn't copy data from the literal.

 foreach(i, ref a; array[2..2+array2.length])
 a[1..1+array2[i].length] = array2[i];

 writefln(array2);
 writefln(array);

 [[1,2,3,4],[5,6,7,8]]
 [[0,0,0,0,0,0],[0,0,0,0,0,0],[0,1,2,3,4,0],[0,5,6,7,8,0],[0,0,0,0,0,0],
 [0,0,0,0,0,0],[0,0,0,0,0,0],[0,0,0,0,0,0],[0,0,0,0,0,0],[0,0,0,0,0,0]]
 --------------------------
 //And for 3D:

 int array[][][];
 array.length=6;
 foreach(ref a; array)
 {
  a.length = 6;
  foreach(ref b; a)
   b.length = 6;
 }

 int array2[][][];


ditto here:
/*
 array2.length=2;
 foreach(ref a; array2)
 {
  a.length = 2;
  foreach(ref b; a)
   b.length = 2;
 }



 array2=[[[1,2],[5,6]],[[9,9],[8,7]]];


could be:

auto array2=[[[1,2],[5,6]],[[9,9],[8,7]]];

 foreach(i, ref a; array[2..2+array2.length])
 foreach(ii, ref b; a[2..2+array2[0].length])
  b[1..1+array2[ii].length] = array2[i][ii];

 writefln(array2);
 writefln(array);
 --------------------------
 ... erm I barely follow it myself :/


Yeah, it's not really that readable :)  Perhaps encapsulating it into a 
function would be more readable.

 I think array can be static and maybe array2 will be as well and I'll 
 manually keep the x,y and z sizes and do normal for-loops over them.


static arrays are different than dynamic arrays, in that they are contiguous 
memory :)  But I think you will still need to set the data in the same way.

-Steve 

bearophile <bearophileHUGS lycos.com> writes:

Saaa Wrote:
 ... erm I barely follow it myself :/


There are ways to shorten your code a little, and/or to make it a bit more
readable. You have to learn still where to put spaces too.

  int array[][];
  array.length=10;
  foreach(ref a; array)
   a.length = 5;


There's this syntax too, if you remember the order of the sizes:
auto array = new int[][][](n1, n2, n3);

foreach(ref a; array)
=>
foreach (ref a; array)

 a[1..1+array2[i].length] = array2[i];


 a[1 .. 1+array2[i].length] = array2[i];


array2.length=2;
=>
array2.length = 2;

In some situations you can use $ instead of length (but not in the code you
have shown, I think).
And you can write yourself a slice(...) function able to perform your complex
slices reducing syntax clutter (but it doesn't support the .. operator, sadly,
as in the .../: of python).

Note that this:
auto a = [[1, 2], [3, 4]];
Isn't the same thing as:
int[][] a = [[1, 2], [3, 4]];
If you use auto the compiler chooses to use a static array.

Bye,
bearophile

"Jarrett Billingsley" <kb3ctd2 yahoo.com> writes:

"bearophile" <bearophileHUGS lycos.com> wrote in message 
news:g6kn24$77v$1 digitalmars.com...

 You have to learn still where to put spaces too.


 foreach(ref a; array)
 =>
 foreach (ref a; array)

 a[1..1+array2[i].length] = array2[i];


 a[1 .. 1+array2[i].length] = array2[i];


 array2.length=2;
 =>
 array2.length = 2;


Don't you think you're being a bit pedantic?  Whitespace is optional and 
everyone has their own preferences. 

bearophile <bearophileHUGS lycos.com> writes:

Rakan Alhneiti:
 I dont think you can do this in any programming language not just D.


I think in NumPy you can do similar things (and maybe in matlab too).

Bye,
bearophile

BCS <ao pathlink.com> writes:

Reply to bearophile,

 Rakan Alhneiti:
 
 I dont think you can do this in any programming language not just D.
 




yes in matlab.