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digitalmars.D.learn - Initialize multi dimensional associative dynamic array

reply "js.mdnq" <js_adddot+mdng gmail.com> writes:
How does one initialize an array defined as

A[B][C] arr;

dynamically? (A,B,C are types, for example, int[int][string])

I want to store an array, indexed by strings, of ints, indexed by 
ints.

For example, What I want is a hash map that maps integers to 
integers so I can do something like

myval = arr[3243];  // has O(1) lookup

But then I want to be able to extend this to use strings to 
subgroup the arrays:


myval1 = arr["Group1"][3243];  // has O(1) lookup
myval2 = arr["Group2"][3243];  // has O(1) lookup


so my arr definition is

int[int][string] arr;

Or, another way to see it, is I want the Key's to be strings and 
the values to be int[int].

But when I try to access the value of the value I get an 
exception, I believe, because I haven't initialized the value. 
(because if I do a simple assign to the value it then works, but 
I'm trying to check if the value exists in the first place)

I've also tried playing around with something like 
int[string[int]] and reversing the order(IIRC the order has to be 
backwards in the definition).
Dec 02 2012
next sibling parent "bearophile" <bearophileHUGS lycos.com> writes:
js.mdnq:


 myval1 = arr["Group1"][3243];  // has O(1) lookup
 myval2 = arr["Group2"][3243];  // has O(1) lookup


Another option is to use an associative array where the keys are 
Tuple!(string, int):

alias Tuple!(string, int) Tkey;
int[Tkey] arr;
myval1 = arr[Tkey("Group1", 3243)];
myval2 = arr[Tkey("Group2", 3243)];

But also take this in account:
http://d.puremagic.com/issues/show_bug.cgi?id=3789



 But when I try to access the value of the value I get an 
 exception, I believe, because I haven't initialized the value. 
 (because if I do a simple assign to the value it then works, 
 but I'm trying to check if the value exists in the first place)


Why don't you show what you are trying to do with a little 
program, plus the errors you get?

Bye,
bearophile
Dec 02 2012
prev sibling next sibling parent "bearophile" <bearophileHUGS lycos.com> writes:
(Maybe this will arrive duplicated, thanks to the forum software)

js.mdnq:


 myval1 = arr["Group1"][3243];  // has O(1) lookup
 myval2 = arr["Group2"][3243];  // has O(1) lookup


Another option is to use an associative array where the keys are 
Tuple!(string, int):

alias Tuple!(string, int) Tkey;
int[Tkey] arr;
myval1 = arr[Tkey("Group1", 3243)];
myval2 = arr[Tkey("Group2", 3243)];

But also take this in account:
http://d.puremagic.com/issues/show_bug.cgi?id=3789



 But when I try to access the value of the value I get an 
 exception, I believe, because I haven't initialized the value. 
 (because if I do a simple assign to the value it then works, 
 but I'm trying to check if the value exists in the first place)


Why don't you show what you are trying to do with a little 
program, plus the errors you get?

Bye,
bearophile
Dec 02 2012
prev sibling parent reply =?UTF-8?B?QWxpIMOHZWhyZWxp?= <acehreli yahoo.com> writes:
On 12/02/2012 06:58 AM, js.mdnq wrote:

 How does one initialize an array defined as

 A[B][C] arr;

 dynamically? (A,B,C are types, for example, int[int][string])


Let me ask a related question: The following initialization does not 
work. Am I doing something wrong?

     int[int][string] arr = [ "hello" : [ 1 : 100, 2 : 200 ] ];

   Error: not an associative array initializer


 I want to store an array, indexed by strings, of ints, indexed by ints.

 For example, What I want is a hash map that maps integers to integers so
 I can do something like

 myval = arr[3243]; // has O(1) lookup

 But then I want to be able to extend this to use strings to subgroup the
 arrays:


 myval1 = arr["Group1"][3243]; // has O(1) lookup
 myval2 = arr["Group2"][3243]; // has O(1) lookup


 so my arr definition is

 int[int][string] arr;

 Or, another way to see it, is I want the Key's to be strings and the
 values to be int[int].

 But when I try to access the value of the value I get an exception, I
 believe, because I haven't initialized the value.


Allow me to repeat what bearophile said: It is very helpful if you show 
such problems in code. Even knowing the type of the exception is very 
helpful. Thanks.


 (because if I do a
 simple assign to the value it then works, but I'm trying to check if the
 value exists in the first place)

 I've also tried playing around with something like int[string[int]] and
 reversing the order(IIRC the order has to be backwards in the 


definition).

This works for me:

void main()
{
     int[int][string] arr;
     arr["hello"] = [ 1 : 100, 2 : 200 ];

     assert("world" !in arr);

     auto hello = "hello" in arr;

     // Note that 'in' produces a pointer:
     assert(typeid(hello) is typeid(int[int]*));
     assert(hello);
     assert(1 in *hello);
     assert(2 in *hello);
     assert(3 !in *hello);
}

Ali

-- 
D Programming Language Tutorial: http://ddili.org/ders/d.en/index.html
Dec 02 2012
parent =?UTF-8?B?QWxpIMOHZWhyZWxp?= <acehreli yahoo.com> writes:
On 12/02/2012 11:27 AM, Ali Çehreli wrote:


 int[int][string] arr;
 arr["hello"] = [ 1 : 100, 2 : 200 ];


Of course, more dynamically:

     int[int][string] arr;

     int[int] a;
     a[1] = 100;
     a[2] = 200;
     arr["hello"] = a;

Ali
Dec 02 2012