[Gambas-user] Sort multidimensional array?

[Gianluigi]

Hi Richard,

See my project DynamicMatrixExample, in Examples of Gambas Software Farm

Regards

Gianluigi

2017-02-07 0:30 GMT+01:00 Tobias Boege <taboege at ...626...>:

> On Mon, 06 Feb 2017, Riccardo wrote:
> > Hi,
> >
> > Is it possible to use the array.sort() method on a two-dimensional array?
> >
> >
> >
> >
> >
> > >         Public arr_Response As New String[][]
> > >
> >
> >
> >
> >
> > Specifically, I'd like to sort the entire array based on the contents of
> the second column something like: arr_Response[][1].sort() ...
> >
>
> You can call String[][].Sort() but the result will probably not be what you
> expect. First of all, you have to understand how Gambas handles the type of
> multi-dimensional array you're using. I have given more explanations of
> this
> on this list and elsewhere than I can recount, but I'll do it another time.
> (I'll type it out anew; search the mailing list archive if you want to see
> previous versions of the explanation.)
>
> The Gambas interpreter can derive array data types from any given data type
> at runtime. Say "X" is any data type that's currently known to the
> interpreter
> (at runtime), then, if you use "X[]" like a data type in your Gambas code,
> the interpreter will notice that "X[]" is made of the known data type "X"
> and a pair of brackets and use a code template to create and register a new
> data type, which is "array of X". "X[]" is a data type created on the fly
> for storing an array of objects of type "X".
>
> The type "String[]" is built-in into the interpreter, but if you use
> "String[][]", the mechanics desribed above are invoked. "String[][]" is a
> new data type created from a code templates stored inside the interpreter.
> This template is, if you care to look at the sources, is really just
> reusing
> the methods of the "Object[]" class.
>
> This means "String[][]" is an "Object[]" which expects to contain elements
> of type "String[]" -- nothing more. This finally explains why
> String[][].Sort() does not do anything sensible. Since the Sort() method
> comes directly from the "Object[]" class, the sorting is done by comparing
> memory addresses of the "String[]" elements. It does not look at the
> Strings
> one layer further down.
>
> So what about your problem? I would advise that you ditch the String[].
> Define a new class "MyResponse" or something, so that you can declare your
> array as
>
>   Public arr_Response As New MyResponse[]
>
> The advantage is that in your own MyResponse class you can implement the
> _compare() special method [1] to compare two MyResponse objects by using
> the second field in the response array, as you originally intended.
>
> After you implement the _compare() method, the Response[].Sort() method
> will sort properly. See also this old project [2] in German, where we
> demonstrate how to sort GridViews (vastly generic, but with some
> restrictions)
> using the very same method. There, the column at which to sort can be
> specified at runtime. Note that the version of the project on this site
> uses a *bad practice* of inheriting Variant[] instead of creating your
> own class. (There may be other shortcomings in that project which I don't
> remember off-hand.)
>
> Regards,
> Tobi
>
> [1] http://gambaswiki.org/wiki/lang/special/compare
> [2] http://www.gambas-buch.de/dw/doku.php?id=k17:k17.7:k17.7.4:start
>
> --
> "There's an old saying: Don't change anything... ever!" -- Mr. Monk
>
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