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digitalmars.D - Array expression for multi dimensional arrays

reply Madhav <unmarshall gmail.com> writes:
Hi,

I tried to do the following:
auto arr = new int[2][2];
arr[] = 1; // using array expressions
// The above gives - Error: cannot implicitly convert expression (1) of type
int  to const(int[2u][])

This was the first step to try out if array arithmetic that worked with single
dimensional arrays worked with multi-dimensional. I guess it does not.

The immediate utility of this would be to cleanly do matrix algebra. Any ideas
why powerful array expressions were not extended to multi dimensional arrays
as well?

Regards,
Madhav
Mar 23 2011
next sibling parent reply spir <denis.spir gmail.com> writes:
On 03/23/2011 12:01 PM, Madhav wrote:

 Hi,

 I tried to do the following:
 auto arr = new int[2][2];
 arr[] = 1; // using array expressions
 // The above gives - Error: cannot implicitly convert expression (1) of type
 int  to const(int[2u][])

 This was the first step to try out if array arithmetic that worked with single
 dimensional arrays worked with multi-dimensional. I guess it does not.

 The immediate utility of this would be to cleanly do matrix algebra. Any ideas
 why powerful array expressions were not extended to multi dimensional arrays
 as well?

 Regards,
 Madhav


IIUC, you can do it level by level only:
unittest {
     int[3] a3;
     int[3][2] a32;
     a3[] = 1;
     a32[] = a3;
     assert(a32 == [[1,1,1], [1,1,1]]);
}

Note: in those assignments, [] is optional, but I consider this as a bug. Even 
more since
    int[3] a3 = 1;	// works
    int[3][2] a32 = a3	// works not

denis
-- 
_________________
vita es estrany
spir.wikidot.com
Mar 23 2011
parent reply Madhav <unmarshall gmail.com> writes:
== Quote from spir (denis.spir gmail.com)'s article

 On 03/23/2011 12:01 PM, Madhav wrote:

 Hi,

 I tried to do the following:
 auto arr = new int[2][2];
 arr[] = 1; // using array expressions
 // The above gives - Error: cannot implicitly convert expression (1) of type
 int  to const(int[2u][])

 This was the first step to try out if array arithmetic that worked with single
 dimensional arrays worked with multi-dimensional. I guess it does not.

 The immediate utility of this would be to cleanly do matrix algebra. Any ideas
 why powerful array expressions were not extended to multi dimensional arrays
 as well?

 Regards,
 Madhav


 IIUC, you can do it level by level only:
 unittest {
      int[3] a3;
      int[3][2] a32;
      a3[] = 1;
      a32[] = a3;
      assert(a32 == [[1,1,1], [1,1,1]]);
 }
 Note: in those assignments, [] is optional, but I consider this as a bug. Even
 more since
     int[3] a3 = 1;	// works
     int[3][2] a32 = a3	// works not
 denis


Yes i guessed that. My question was more to do with extending array expressions
for multi dimensional arrays as well.
Don't you think this should be provided by the language? It will ease out a lot
of
mathematical implementations

Regards,
Madhav
Mar 23 2011
parent Don <nospam nospam.com> writes:
Madhav wrote:

 == Quote from spir (denis.spir gmail.com)'s article

 On 03/23/2011 12:01 PM, Madhav wrote:

 Hi,

 I tried to do the following:
 auto arr = new int[2][2];
 arr[] = 1; // using array expressions
 // The above gives - Error: cannot implicitly convert expression (1) of type
 int  to const(int[2u][])

 This was the first step to try out if array arithmetic that worked with single
 dimensional arrays worked with multi-dimensional. I guess it does not.

 The immediate utility of this would be to cleanly do matrix algebra. Any ideas
 why powerful array expressions were not extended to multi dimensional arrays
 as well?

 Regards,
 Madhav


 IIUC, you can do it level by level only:
 unittest {
      int[3] a3;
      int[3][2] a32;
      a3[] = 1;
      a32[] = a3;
      assert(a32 == [[1,1,1], [1,1,1]]);
 }
 Note: in those assignments, [] is optional, but I consider this as a bug. Even
 more since
     int[3] a3 = 1;	// works
     int[3][2] a32 = a3	// works not
 denis


 
 Yes i guessed that. My question was more to do with extending array expressions
 for multi dimensional arrays as well.
 Don't you think this should be provided by the language? It will ease out a
lot of
 mathematical implementations


The problem is, that with the multi-dimensional case, you generally want 
STRIDED operations. These are much more complicated, and are much easier 
to implement in a library rather than in the core language.

Belongs in Phobos, no doubt about it. Currently waiting for the 
enhancement patch in bug 3474 to be applied.
Mar 23 2011
prev sibling next sibling parent Jonathan M Davis <jmdavisProg gmx.com> writes:
 Hi,
 
 I tried to do the following:
 auto arr = new int[2][2];
 arr[] = 1; // using array expressions
 // The above gives - Error: cannot implicitly convert expression (1) of
 type int  to const(int[2u][])
 
 This was the first step to try out if array arithmetic that worked with
 single dimensional arrays worked with multi-dimensional. I guess it does
 not.
 
 The immediate utility of this would be to cleanly do matrix algebra. Any
 ideas why powerful array expressions were not extended to multi
 dimensional arrays as well?
 
 Regards,
 Madhav


It wouldn't really help in this case, but I would point out that you probably 
didn't declare the type of array that you meant to (you might have, but most 
people wouldn't really want the type of array that you declared but _would_ 
mistakenly use the syntax that you used).

You declare an int[2u][], whereas what you probably wanted was an int[][]. You 
have a dynamic array of static arrays where each static array has a fixed 
length of 2. If you want a dynamic array of dynamic arrays, you need to do 
this:

auto arr = new int[][](2, 2);

- Jonathan M Davis
Mar 23 2011
prev sibling parent Daniel Green <venix1 gmail.com> writes:
On 3/23/2011 7:01 AM, Madhav wrote:

 Hi,

 I tried to do the following:
 auto arr = new int[2][2];
 arr[] = 1; // using array expressions
 // The above gives - Error: cannot implicitly convert expression (1) of type
 int  to const(int[2u][])

 This was the first step to try out if array arithmetic that worked with single
 dimensional arrays worked with multi-dimensional. I guess it does not.

 The immediate utility of this would be to cleanly do matrix algebra. Any ideas
 why powerful array expressions were not extended to multi dimensional arrays
 as well?

 Regards,
 Madhav


I'm not sure this applies to your topic, but it gave me something to 
play with that may be related.

Static arrays are always laid out contiguously in memory.  This appears 
to allow casting to a single dimensional array.

     auto a = new int[3][2];
     int[] test = cast(int[]) a;
     printf("%d\n", test.length); // Equals 6.
Mar 23 2011