CODEWITHSUNDEEP
arraysadaarrayofarrays
Yellowjacket11
Yellowjacket11

Reputation: 71

Creating an array of empty arrays in Ada

I am trying to write an Ada equivalent of the following statement in Python: L = [[] for i in range(n)]

I am solving a dynamic programming problem and my plan is to eventually copy the contents of the jth array inside L into the ith array (j < i) if the ith array has fewer elements than the jth array.

I have found how to create an empty array by defining its range in the reverse order. So, for instance, arr2 would be an empty array created as follows:

arr2: array(2 .. 1) of Integer;

My question is, how do I define the bigger array L to include n of such arr2 arrays?

Please let me know.

Update: I was able to get it correctly working using the answers below. Here is my code.

package Integer_Vectors is new Ada.Containers.Vectors
    (Index_Type   => Natural,
    Element_Type => Integer);

    N: Integer;

    Array_Of_Vectors : array(1 .. N) of Integer_Vectors.Vector := (others => Integer_Vectors.Empty_Vector);

    Input_Sequence: Integer_Vectors.Vector;

    Max: Integer_Vectors.Vector;

    Input_List : String := Get_Line;

    IntCast : Integer;

    Last : Positive := 1;
    
    begin

    while Last < Input_List'Last loop
        Get(Input_List(Last..Input_List'Last),IntCast,Last);
        Input_Sequence.Append(IntCast);
        Last := Last + 1;
    end loop;
    
    N := 0;

    for i of Input_Sequence loop
        N := N + 1;
    end loop;

Upvotes: 4

Views: 1373

Answers (1)

Maxim Reznik
Maxim Reznik

Reputation: 1417

In Ada L will be

L : array (1 .. N, 1 .. 0) of Integer;

But it's useless, because you won't be able to extend it latter. @Zerte is right.

You can use a vector on indefinite elements, for instance. Like this

with Ada.Containers.Indefinite_Vectors;

type Integer_Array is array (Positive range <>) of Integer;

Empty : constant Integer_Array := (1 .. 0 => <>);

package Integer_Array_Vectors is new
 Ada.Containers.Indefinite_Vectors
   (Index_Type => Positive, Element_Type => Integer_Array);

L : Integer_Array_Vectors.Vector;

L.Append (Empty, N);

if L (J)'Length > L (I)'Length then
   L.Replace_Element (I, L(J));
end if;

Upvotes: 7

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