       # set manipulation

```Hello everyone,
I have a problem with data set manipulation. I have a data set;
data2D={{1.3,2.4},{1.4,5.6},{ ,},{ ,}     }}
<<DiscreteMath`ComputationalGeometry` delval=DelaunayTriangulation.

The set delval gives the nearest neighbour of each of the data2D
points.Thus delval may look like:

delval={{1,{2,5,6}},
{2,{3,6,4}},
{3,{2,4 1}},
}}
In the set delval 1=ist point in data2D (i.e in above eg. {1.3,2.4})
2=2nd point
3=3rd Point
and so on.
Thus 1st point has it's nearest neighbour as 2nd, 5th, 6th points.

Now I have to calculate the angle of the lines joining point 1 with it's
nearest neighbour, with the x-axis=>

angle=TanInverse[y(2)-y(1)/(x(2)-x(1))], where for sake of explanation
point1={x(1),y(1)}, point2={x(2),y(2)}  and so on for points 5,6.
This should be done for all the points of data2D.

Then I need to add the angles corresponding to each point and then find
the average .
So If anyone who could give a slight hint of how this sort of data
manipulation can be done , I would be extremely grateful , Thnking you,

Yours Sincerely,
Nilay Saha
Kamerlingh Onnes Lab,
2300RA Leiden
Postbus: 9506,
The Netherlands.
Phone:
(0031)71 5275476.

```

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