CFD Online Discussion Forums - dynamic list (variable size)

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dynamic list (variable size)

Hello,

I have a list of scalars with unknown size at declaration time. During the simulation I want to remove given elements from the list at different times.

I know that you can define a DynamicList (DynamicList<scalar> test;) and then add some values (test.append(value)), clear the list (test.clear()) or maybe delete the last introduced value. The thing is if I need to delete some elements from the list It occurs to me to make a temporal copy with the new size or something like that.

So my question is... what is the best strategy to declare a list of scalars which is expected to delete some given elements (and then varying the size of the list)? How can I do it effectively?

Thank you in advanced.

Regards.

edit: the post is similar was treated before here and there's an interesting reply:

Quote:

Originally Posted by deepsterblue (Post 423118)

Georg,

DynamicList only allows appends and removal to/from the end of the list (think of a stack-like operation). If you're looking to remove from the middle, you'll have to resort to a copy to another list (followed by a List::transfer).

This might boil down to an appropriate choice of container - if you're looking to frequently remove arbitrary items from a list, a linked-list or hash table may be a better option.

Someone can explain it in detail?

Depends. What is the size of your list, how often will you be deleting elements and how many will you remove?

Hello Laurance.

The list has a size in a range 100-1000 and I need to remove 1 element each time I check a condition. Every timestep It can happen for around 10-70% of the size of the list. (Eg: size 300, 40 elements to remove in a timestep).

Thank you for your hints.

That's quite small. I'd either use a HashTable if you have to remove elements individually, or if you can remove them as a block then do this:

Code:

PackedBoolList elemToRemove(l.size());



forAll(l, i)

{

    if (checkCondition)

    {

        elemToRemove[i] = true;

    }

}



inplaceSubset(elemToRemove, l);

I don't have experience using HashTable, I actually need to remove elements individually from Dynamic and Sortable lists. I'm going to review everything with this new feedback.

Thanks.

Here is how I did it to have a pairs of labels and scalars defined as a HashTable. With this new method I can efficiently remove an element. There's a strange issue, I'm using the findLower function but the problem comes when I erase a element of the HashTable the findLower still points to the removed index. I have checked that the element was erased correctly (apparently at least debugging) and the the size reduced.

I show an example:

Code:

    HashTable<scalar, label> testHash_;



    //- insert values with key 1, 2 and 3

    testHash_.insert(1,0.5);

    testHash_.insert(2,0.7);

    testHash_.insert(3,0.3);



    //- print HashTable

    Info << "testHash: " << testHash_ << nl << endl;



    //- find value lower than 0.6

    label j = findLower(testHash_,0.6);



    //- erase key j and his value

    testHash_.erase(j);



    //- print HashTable

    Info << "testHash: " << testHash_ << nl << endl;



    //- find another value lower than 0.6

    label k = findLower(testHash_,0.6);



    //- erase key k and his value

    testHash_.erase(k);



    Info << "testHash: " << testHash_ << nl;

OUTPUT

Code:

testHash: 

3

(

3 0.3

1 0.5

2 0.7

)



testHash: 

2

(

3 0.3

2 0.7

)







--> FOAM FATAL ERROR: 

1 not found in table.  Valid entries: 2(3 2)

still looking for key 1!!

The topic of the post has been resolved for me, thank you very much! Still I have that thing but maybe I made a mistake.