Comparing ranges

re: Comparing ranges

Ryan Farley — Thu, 19 Aug 2004 18:03:00 GMT

Awesome Jay. I agree that my way was riddled with "code smell", but it was more the algorithm I was after, not focused on the implementation (that was up to my friend who called me about this).

I love how you did this as a range class using generics. Very cool stuff!

Intersection of Date Ranges

{ public virtual blog; } — Fri, 20 Aug 2004 00:48:00 GMT

A friend of mine called me yesterday about a scheduling application he is working on. His question was so simple, or so it seemed, but it really drove me nuts. Basically he just wanted to find out if two date ranges intersected at all. Simple enough. It was one of those kinds of answers that you immediately start rattling off the solution, but every thing that started to come out of my mouth was failing my mental unit testing. I'll admit it threw me for a loop for a short bit.

re: Comparing ranges

Dithermaster — Thu, 19 Aug 2004 21:55:00 GMT

Indeed. A friend approached me years ago about finding if a time range overlaps. There are just so many cases. However, (and the "ah ha!" moment), it's *much* easier to find out of they DON'T overlap, and negate that.

In other words (in C):

overlap = ! ( (end2 < start1) || (start2 > end1) );

Easy.

///d@

RE: Comparing ranges

Ryan Farley — Thu, 19 Aug 2004 22:49:00 GMT

Dithermaster, very nice.

re: Comparing ranges

James Manning — Fri, 20 Aug 2004 00:37:00 GMT

if (left.Start.CompareTo(left.Start) == 0)
{
return true;
}

Maybe it's just a typo in reproduction, but maybe we should add some negative tests and not just 5 positive ones? :)

re: Comparing ranges

mikeb — Fri, 20 Aug 2004 03:39:00 GMT

In addition to the typo

if (left.Start.CompareTo(left.Start) == 0)

another problem happens if the start and end of a range are out of order.

Range<int>( 4, 1) and Range<int>( 2, 1) overlap, but I believe the presented code would not detect this.

Either the Range<T> constructor need to enforce left <= right, or the overlap check needs to handle this situation.

re: Comparing ranges

Matthew W. Jackson — Fri, 20 Aug 2004 04:51:00 GMT

I'd vote for the constructor enforcing the order. This would let you create ranges out of variable-data, which may or may not be in the right order (imagine dragging the mouse to select a range on a timeline), and have the Range automatically be in the correct order.

Besides I'm a little biased, because that's how MY Range (recently upgraded to Range<T>) struct works. But it also does a LOT of other nifty things.

re: Comparing ranges

Thomas Eyde — Fri, 20 Aug 2004 13:22:00 GMT

Isn't this as easy as to verify if one value is inside the range?

Overlap(a, b){
return IsInside(a) || IsInside(b);
}

IsInside(a) {
return IsBetween(a, this.a, this.b) || IsBetween(a, this.b, this.a);
}

IsBetween(c, a, b) {
return a <= c && c <= b;
}

Building a generic Range class

Coding Sanity — Thu, 31 May 2007 20:41:13 GMT

Quite a long article where I discuss the creation of a generic Range class, and go into the decisions and thinking about many of the design aspects. Touches on lambdas, iterators, generics, and the usual rambling grab-bag of stuff I go on about when I

jaybaz MS WebLog Comparing ranges | alternative dating

jaybaz MS WebLog Comparing ranges | alternative dating — Wed, 17 Jun 2009 10:09:41 GMT

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