<![CDATA[qBinaryFind for QStringList]]>I have 2 QStringLists (L1 is a subset of L2). I need to find the index of all L1 elements in L2. I am using binary search to do the same but I am not sure how to find the index. Also, please do suggest if there is a better way for doing the same.

Thanks.

 for(int i=0;i<filesGeotagged.length();i++){

        QList<QString>::iterator k = qBinaryFind(L2.begin(),L2.end(),L1[i]);
        qDebug() << *k;

    }
]]>https://forum.qt.io/topic/73845/qbinaryfind-for-qstringlistRSS for NodeThu, 09 Apr 2026 22:00:33 GMTTue, 29 Nov 2016 11:45:55 GMT60<![CDATA[Reply to qBinaryFind for QStringList on Wed, 30 Nov 2016 12:00:38 GMT]]>@mrjj

It works !! Thanks.

]]>https://forum.qt.io/post/362379https://forum.qt.io/post/362379Wed, 30 Nov 2016 12:00:38 GMT<![CDATA[Reply to qBinaryFind for QStringList on Tue, 29 Nov 2016 15:41:53 GMT]]>Your approach is sound. The only drawback is you'd need to sort L2 (before starting the search) for obvious reasons. Another thing you can try if your lists are long is to hash L2. For example:

// Preparation part:
QHash<QString, int> indices;
indices.reserve(L2.size());
for (qint32 i = 0, size = L2.size(); i < size; i++)
    indices.insert(L2.at(i), i);

// Search part:
for (qint32 i=0, size = filesGeotagged.length(); i < size; i++)  {
    qDebug() << indices.value(L1.at(i), -1); // Output the index, handle -1 as an error (i.e. put an assertion)
}
]]>https://forum.qt.io/post/362218https://forum.qt.io/post/362218Tue, 29 Nov 2016 15:41:53 GMT<![CDATA[Reply to qBinaryFind for QStringList on Tue, 29 Nov 2016 11:52:20 GMT]]>Hi
Not tested with Qt but
Can you do

int index=(k - L2.begin());
?

You could also use a map, if each L1 element has a good key.
Then it would be direct lookup.

]]>https://forum.qt.io/post/362188https://forum.qt.io/post/362188Tue, 29 Nov 2016 11:52:20 GMT