Re: Tally

[Brad Moore <bmoore.ada@gmail.com>]

On Tuesday, January 14, 2020 at 2:08:16 PM UTC-7, Jeffrey R. Carter wrote:

> A lot depends on what restraints the problem domain puts on the input values. If 
> you can define something like
> 
> type Input_Number is range 1 .. 10;
> 
> then you can do something straightforward like
> 
> type Count_Map is array (Input_Number) of Natural;
> 
> Count  : Count_Map := (others => 0);
> Number : Input_Number;
> ...
> loop
>     exit when No_More_Numbers;
> 
>     Number := Next_Number;
>     Count (Number) := Count (Number) + 1;
> end loop;
> 
> If you can't limit the input numbers to a sufficiently small range that an 
> object like Count can be declared, then you'll need to use a map, as Holsti 
> suggested, which is only a little more complicated.
> 

Just to clarify, I'd say using a Map is more complex (quite a bit actually) in terms of what is happening semantically when the program executes, but I think it is worth noting that there is not necessarily much difference in complexity in terms of what the user has to write. As Jeff notes, using a map does has the advantage of flexibility, for example in handling sparsely populated data where there is a large range of input values.

e.g.

with Ada.Containers.Ordered_Maps; use Ada;

procedure Main
is
   package Count_Maps is new
     Containers.Ordered_Maps (Key_Type     => Natural,
                              Element_Type => Natural);
   
   type Input_Data is array (Natural range <>) of Natural;
   
   Input : Input_Data := (2, 3, 8, 2, 2, 2, 7, 2, 3, 4, 8);
   
   Counts : Count_Maps.Map;
      
begin
   for Number of Input loop
      Counts (Number) := Counts (Number) + 1;
   end loop;
end Main;

Brad