03.05.2017, 21:09, "Sean Harmer" <sean.har...@kdab.com>: > Hi, > > On 03/05/2017 17:57, Jason H wrote: >> I have a app that does a lot of numeric processing,using quint32, qreal >> mostly (and occasional QVector3D). 10k-1M items in the data set. I generally >> do know the size of the dataset before I start adding to it, so I call >> reserve() on it. Given that, and that I've been using QMap and QVector, when >> I use QMap and want the keys() it gives me a QList, which I then have to >> call toVector() on. >> >> So this leads me to ask if I should be using QList all this time? I had >> thought that QList was considered harmful. [1][2][3] >> But "everything" seems to return to me a QList, rather than a QVector. >> >> What should I be using? (I'm Targeting 5.8 and later.) > > Depends upon your usage patterns. Do you do a lot of map operations over > the vectors/maps? If so cache coherency may well be the biggest factor, > in which case QVector or even std::vector may give you better > performance than QMap. Given the current discrepancy between CPU speeds > and memory access latencies it's hard to do better than a vector for > pure performance as the contiguous memory layout makes better use of the > L2 cache.
B or B+ trees tend to be more cache-friendly than red-black trees (QMap), yet allowing faster inserts http://panthema.net/2007/stx-btree/ (in-memory B+ tree implementation) https://code.google.com/archive/p/cpp-btree/ (in-memory B tree implementation) Don't believe those how will tell you that B-tress are only for storage :) > > If ease of API use is your main concern then QMap may be a better fit. > It all depends what you are using this data for. > > Cheers, > > Sean > > -- > Dr Sean Harmer | sean.har...@kdab.com | Managing Director UK > KDAB (UK) Ltd, a KDAB Group company > Tel. +44 (0)1625 809908; Sweden (HQ) +46-563-540090 > Mobile: +44 (0)7545 140604 > KDAB - Qt Experts > _______________________________________________ > Interest mailing list > Interest@qt-project.org > http://lists.qt-project.org/mailman/listinfo/interest -- Regards, Konstantin _______________________________________________ Interest mailing list Interest@qt-project.org http://lists.qt-project.org/mailman/listinfo/interest
