[Gambas-user] Rename a Collection Key retaining the order

[Bruce Steers]

On Sun, 9 Jan 2022 at 22:03, Tobias Boege via User <
user at lists.gambas-basic.org> wrote:

> On Sun, 09 Jan 2022, Bruce Steers wrote:
> > Is there a simple way to rename a collection key name but retain the
> order?
> >
> > I found i can rename it using Swap but it pops the item at the and of the
> > collection index.
> >
> > Best i have so far is this fuction that copies and returns the collection
> > with a preserved order.
> > so if my second collection item had the key "t2" I can do this...
> >
>
> Your copy solution is the only one I can come up with. While looking at
> the wiki and source code, I noticed that the Collection.Key property
> used in the For Next loop is a read/write property, but I found no use
> of that fact...
>
> As you are undoubtedly aware, the hash table datatype that Collection
> implements in Gambas is usually an unsorted "pile of data" that has some
> internal structure facilitating the lookup of data by a string. The fact
> that Gambas guarantees that keys are maintained in insertion order and
> that iteration always uses this order is a small bonus, but this is more
> of an addon than a really exposed feature. You're experiencing this right
> now because while it's technically possible to do this efficiently in the
> current implementation, there is no API to rename a key without changing
> its place in the key order.
>
> If changing keys is something you do often and do on big Collections,
> then copying is wasting time. If you experience performance problems
> with the copy solution, then consider making a new class explicitly for
> managing "a mapping from string key to variant data with an ordering
> on the keys". This class would contain a normal Collection and a String[],
> where the String[] contains all keys in their desired ordering (and you
> ignore the ordering that Collection keeps).
>
> You have to keep both data structures in sync through all modifications
> that the user makes (e.g. _put, Add, Remove, any other methods you add),
> but if you manage that, you can add your own API to modify a key (inside
> the String[]) without affecting its ordering because the algorithms in
> your class will always consult the String[] for the ordering of its keys.
>
> This will use more memory because you effectively store all the keys
> once more in the String[], but changing a key will be vastly faster than
> to recreate the whole Collection. It all depends on how large your data
> is and how frequently you expect to have to change keys.
>
> Best,
> Tobias
>

Aah i see , thanks for the info :)

the demand (on the computer) is not so bad i think for the application i
have for it.

It's for [Desktop Action ] items in the DesktopFile.class
i've written a new class to handle a .desktop files [Desktop Actions] with
ease :)
https://gitlab.com/bsteers4/gambas/-/tree/DesktopActions.class

I guess essentially it does not matter if the [Desktop Action ] order does
not match the Actions order but i think it would make for a neater file if
it is.

Most launchers will not have many actions set so the speed i think will not
matter much.  a reasonable compromise for things nicely in order :)
Thanks again :)
BruceS
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