Find index of QVector by comparing an item

Yash

Hi,

I want to compare a item in a QVector and that will return index.

Ex. QVector {20,45,57,89} [0,1,2,3]

for value 46 it should say 2

for value 21 to 45 it should return 1

I can do this by using some loop conditions. But I want to know is there any inbuilt function for this.

Smar

http://doc.qt.nokia.com/latest/qvector.html#indexOf

Yash

This is not my problem. I know that how to find index of an item .

My Question is to find index of item which is in range not exactly there.

Like 46 is nowhere still it returns 2 and not -1 like above func.

Hope it clears me more.

Yash

Consider any type of container like QVector or QList any item which can solve my problem.

ivan

Since this is applicable only to sorted vectors, it would be strange if there existed a method like that in a QVector.

You can easily implement it via a binary search.

Yash

yea that's what I was thinking i.e binary search but I was looking for any easy solution(s).

BS is in qt.

Link is "Binary search in QT":http://doc.trolltech.com/qq/qq15-qalgorithms.html

ivan

Well, I don't think you'll be able to use the built-in BS. (you are not looking for an exact match).

Alternatively, you can go wild :) and implement a Range class and overload some operators... but I think it would be too much hassle for something like this.

Yash

Agreed

I'm doing with core c++.

Will post solution here for other guys.

tzander

Such a list has been implemented by a troll before and is available here

http://qt.gitorious.org/qt-labs/itemviews-ng/blobs/master/src/qsectionspans_p.h

janarve

I think what you are looking for is qLowerBound (or qUpperBound). It does a binary search, and returns the position where the item should be inserted, regardless of if the item is found or not.

tzander

Just want to add that QMap has upperBound and lowerBound as methods directly; which is a bit nicer to me than using a global method ;)

Yash

QMap is perfect solution in this case.

I'm little late .... :)

Thanks guy!