December 02, 2012
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).
December 02, 2012
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
December 02, 2012
(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
December 02, 2012
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

December 02, 2012
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

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