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how to find overlapping intervals?

Asked by Itzik on 14 May 2013

Hi, is there a function or an efficient way to find the overlap between two intervals represented in vectors. for example for a=[0 90 180 270]; and b=[26,180,270]; it should find the following overlaps and return the indices

26,90 (2,1) 90,180 (2,2) 180,270 (3,3) or (4,2) and the edges as well (as though the intervals are cyclic) 270,0 (1,4) 0,26 (1,1)

thanks

1 Comment

Jan Simon on 14 May 2013

I'm not sure, what "26,90 (2,1) 90,180 (2,2)..." should mean. Of course this notation is clear to you, but an exact definition for the forum would be a good idea also.

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Answer by Cedric Wannaz on 14 May 2013
Edited by Cedric Wannaz on 14 May 2013

If boundaries are integer, a solution can built based on CUMSUM for building interval IDs and DIFF or UNIQUE for finding boundaries and IDs. I can develop this further if you are interested.

However, if all you have to do is to generate the list of intervals, without really caring for interval IDs, why couldn't you just go for something simpler, like:

``` >> bnd = unique([a, b]) ;
>> if bnd(end) < 360,  bnd = [bnd, bnd(1)] ;  end
>> int = [bnd(1:end-1); bnd(2:end)]
int =
0    26    90   180   270
26    90   180   270     0 ```

Answer by Thomas on 14 May 2013

Your question is a little ambiguous but her is something you can use

` doc intersect`

To see where the arrays overlap

```[C,ia,ib]=intersect(a,b)
```

Ans

```C =
180.00        270.00
ia =
3.00          4.00
ib =
2.00          3.00
```

1 Comment

Itzik on 14 May 2013

i found this function too. but it doesnt doo what i mean. it finds equal parameters and not intervals. ill try to be more clear. imagine a straight line. this line begins at the first value of vector a. (in my example 0). the next point on tha line is defined by the second value in a (in my example 90) and so on... now imagine a second straight line right under the first one. this line is defined by the values in b. now if we draw vertical lines in each point of the lines we get areas whih overlap. the overlap is defined by a right and left vertical lines, each belongning to a different vector. was that more clear?

Answer by Jan Simon on 14 May 2013