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!