[Qt-interest] New container class needed in Qt

[Mandeep Sandhu]

On Tue, Oct 18, 2011 at 11:45 AM, Roopesh Chander <roop at forwardbias.in> wrote:
> In your case, you seem to be looking for ordering in terms of one key
> (insertion time/order) and lookup in terms of another key (A/B/C). It's not
> possible to achieve this without using an additional index (that stores
> ordering based on the second key).

Actually, I was looking for something like what Python has - an
ordered dictionary:

http://docs.python.org/library/collections.html#collections.OrderedDict

Maybe we should have a similar equivalent in Qt as well? :)

>
>   // for lookups
>   QHash<QString /*A*/, QPair<QString /*Apple*/, int /*insertion order*/>
> hash;
>   // for insertion order
>   QMap<int /*insertion order*/, QString /*A*/>;
> where we can cap deletion time to O(log n).

Thanks, this approach looks promising.

-mandeep

> roop.
> On Tue, Oct 18, 2011 at 11:04 AM, Mandeep Sandhu
> <mandeepsandhu.chd at gmail.com> wrote:
>>
>> Hi All,
>>
>> I have a requirement where I want a Map/Hash like container on which I
>> can do key based lookups but also have the items stored in the order
>> in which they were inserted.
>>
>> To elaborate, I'll detail my requirement with a simple example.
>>
>> Consider that we have received a list of items from some external
>> source. The list contains strings in a particular order, eg: ["D",
>> "B", "A" , "C"].
>>
>> I want to however, store some associated values along with each item
>> of the list. eg:
>> A - "Apple"
>> B - "Ball"
>> C - "Cat"
>> D - "Donkey" :)
>>
>> I want to store this in a dictionary like structure because I would
>> want to later 'lookup' the associated values with a given key
>> (A/B/C..).
>>
>> If I simply store it in a QMap, I can do lookups, but then the items
>> would get sorted alphabetically (A,B,C,D). However I want to preserve
>> the order of the keys. So using a QHash or QMap won't work.
>>
>> A way of achieving the require behavior is to use a List, so that the
>> order of keys is preserved. But then there's no easy way to lookup any
>> arbitrary value (apart from iterating the list).
>> I don't want to maintain 2 structures (a list for keeping track of key
>> order and a map for value lookup).
>>
>> Any suggestions about how existing container classes can be used to
>> achieve this?
>>
>> Thanks,
>> -mandeep
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>
>