Creating an array of unique elements

[Guilherme Vieira]

Ah, yeah. I think you're right. Set is exactly what I need, and the fact
that it works with hashes is even better. A pity D still doesn't have it,
since it looks very useful, but thanks for your response. I'll take a look
at your implementation later.

Is there any prevision for sets in core D or Phobos?

-- 
Atenciosamente / Sincerely,
Guilherme ("n2liquid") Vieira


On Mon, Dec 27, 2010 at 11:39 AM, spir <denis.spir at gmail.com> wrote:

> On Mon, 27 Dec 2010 05:22:14 -0200
> Guilherme Vieira <n2.nitrogen at gmail.com> wrote:
>
> > Right now I'm wondering how's the best way to create a dynamic array
> object
> > which will only accept "unique" elements (i.e., elements != from the
> > existing elements in the array).
>
> (Take my words with precaution because I don not know D very well myself.)
>
> Hello Guilherme. If I understand your purpose correctly, what you're trying
> to define is a set, not an array, in the common sense of the terms in
> programming. To ensure uniqueness, you'd need to check whether the element
> exits already, which can only be very slow using an array (O(n)): you need
> to traverse the array element per element. Sets instead are build using data
> structures that allow this check to be far faster, by looking up a given
> element in a more clever way.
>
> There is no builtin Set type in D yet. The simplest way (and maybe the
> best) would be use associative arrays where keys would be actual elements
> and values just fake. (e in set) would tell you what you need. Depending on
> your requirements, trying to put an existing element would just put it again
> with no change, or should throw an error. In the latter case, you need to
> check it yourself or build a wrapper type (struct or class) around builtin
> associative arrays.
>
> For instance:
>    Existence[Element] set;
>    Element[] elements = ['a','c','e'];
>    Element[] values = ['a','b','c','d','e'];
>    foreach (element ; elements)
>        set[element] = EXISTS;
>    // Note: 'in' actually return a pointer to element.
>    foreach (value ; values)
>        writeln(cast(bool)(value in set));
>
> Note: I have a Set type in stock at
> https://bitbucket.org/denispir/denispir-d/src/b543fb352803/collections.d,
> but wonder whether it's really necessary given the above. But you can have a
> look to see how it's done (this would give you some hints about "language
> methods" called 'opSomething', see TDPL's index).
>
>
> Denis
> -- -- -- -- -- -- --
> vit esse estrany ☣
>
> spir.wikidot.com
>
>
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