How to sort QList<QList<QVariant>>

[JonB]

@leinad said in How to sort QList<QList<QVariant>>:

So why when assigning a QSortFilterProxyModel to a view is loading the model so slow? Does the proxymodel index the data somehow?

Yes, and it does sorting/filtering so it's slower. I cannot say whether the slowness you see at 100,000 rows is right or not, I guess sorting that takes a bit of time.

If you are happy to sort the underlying model explicitly and omit QSortFilterProxyModel you can do that, e.g. via the std::sort() @VRonin has typed in.

[leinad]

Thanks. Is there anyway have it sort at the end of the load rather than as it goes? Why is it when I used to use QStandardItemModel and sorted using the treeView it was so much faster? The load was fast too. What happens under the covers using QstandardItemModel that makes such a difference?

[leinad]

Well, it looks like Vronin solution worked. I got rid of the proxyModel and attached the view directly to QAbstractTableModel and implemented the sort after the load. It loads and sort very quickly. Now I need to create a signal and slot mechanism to check when a user clicks on a particular column on the view for sorting which I will implement via std::sort.

Thanks.

[VRonin]

@leinad said in How to sort QList<QList<QVariant>>:

Now I need to create a signal and slot mechanism to check when a user clicks on a particular column on the view for sorting which I will implement via std::sort.

No need to create anything fancy, just reimplement QAbstractItemModel::sort do do the sorting you want and everything else will be handled automatically by Qt

void MyModel::sort(int column, Qt::SortOrder order = Qt::AscendingOrder){
emit layoutAboutToBeChanged({QModelIndex()}, QAbstractItemModel::VerticalSortHint);
std::sort(list.begin(),list.end(),[column,order](const QList<QVariant>& a, const QList<QVariant>& b)->bool{
if(order == Qt::AscendingOrder)
return a.at(column)<b.at(column);
return a.at(column)>b.at(column);
});
emit layoutChanged({QModelIndex()}, QAbstractItemModel::VerticalSortHint);
}

[leinad]

That is exactly what I did except for:

emit layoutAboutToBeChanged({QModelIndex()}, QAbstractItemModel::VerticalSortHint);

[leinad]

@VRonin said in How to sort QList<QList<QVariant>>:

emit layoutChanged({QModelIndex()}, QAbstractItemModel::VerticalSortHint);

VRonin,

I have another question. Would you know how to handle this case in a sort? It seems to work okay when using QStandardItemModel sorting under Qt but not with the above sorting.

So the sorting works fine as is where we sort properly on column 1 which gives us the bottom results. But now within that sort I'd like to sort name1 further using column2 so name1 and name 2 is rearranged in column2 order.
If column1 is not a duplicate within the column 0 grouping then no further sort is required. So essentially take the first sort and for duplicate column 0 and column1 values resort using column 2. Is this possible?

Example:
Think of column 1 as time (consider a string) where we have row data for the same object name with duplicate time, and column 2 is the rowID from a database. So even though technically the sort is correct by time the exact order in the database is governed by the rowID from a database. Essentially sort by time and then by RowID for objects in column0 and 1 that have the same value. For some reason QStandardItemModel handles this all by itself so it would be nice if I can recreate it.

column 0 column1 column2
name1 123 3
name1 123 1
name1 123 2
name2 345 2
name2 345 3
name2 345 1

result:
name1 123 1
name1 123 2
name1 123 3
name2 345 1
name2 345 2
name2 345 3

[VRonin]

@leinad said in How to sort QList<QList<QVariant>>:

For some reason QStandardItemModel handles this all by itself

It doesn't. It probably just uses std::stable_sort instead of std::sort.

In any case this case is trivial, the comparison function can take care of it.
Using your example:

void MyModel::sort(int column, Qt::SortOrder order = Qt::AscendingOrder){
emit layoutAboutToBeChanged({QModelIndex()}, QAbstractItemModel::VerticalSortHint);
std::sort(list.begin(),list.end(),[column,order](const QList<QVariant>& a, const QList<QVariant>& b)->bool{
const auto aV = a.at(column);
const auto bV = b.at(column);
if(order == Qt::AscendingOrder)
return aV==bV ? aV<bV : a.at(2)<b.at(2);
return aV==bV ? aV>bV : a.at(2)>b.at(2);
});
emit layoutChanged({QModelIndex()}, QAbstractItemModel::VerticalSortHint);
}

[leinad]

Thank you! I'll try it.

[leinad]

@VRonin said in How to sort QList<QList<QVariant>>:

mit layoutAboutToBeChanged({QModelIndex()}, QAbstractItemModel::VerticalSortHint);
std::sort(list.begin(),list.end(),[column,order](const QList<QVariant>& a, const QList<QVariant>& b)->bool{
const auto aV = a.at(column);
const auto bV = b.at(column);
if(order == Qt::AscendingOrder)
return aV==bV ? aV<bV : a.at(2)<b.at(2);
return aV==bV ? aV>bV : a.at(2)>b.at(2);
});
emit layoutChanged({QModelIndex()}, QAbstractItemModel::VerticalSortHint);

Unfortunately this does not work.
According to the code you have we don't sort on column at all. We first have to sort on column and once that is done, then we resort all duplicates of column values to some other column.

[VRonin]

I just inverted the 2 siders of :, it's trivial to fix:

void MyModel::sort(int column, Qt::SortOrder order = Qt::AscendingOrder){
emit layoutAboutToBeChanged({QModelIndex()}, QAbstractItemModel::VerticalSortHint);
std::sort(list.begin(),list.end(),[column,order](const QList<QVariant>& a, const QList<QVariant>& b)->bool{
const auto aV = a.at(column);
const auto bV = b.at(column);
if(order == Qt::AscendingOrder)
return aV==bV ?  a.at(2)<b.at(2) : aV<bV;
return aV==bV ? a.at(2)>b.at(2) : aV>bV;
});
emit layoutChanged({QModelIndex()}, QAbstractItemModel::VerticalSortHint);
}