Random with Weighted results

Question

Hi All, 
 I was wondering if anyone knew how to write the statement for a weighted random generator. 
 I have a series of polygons that I am changing the colour of using just a simple Random(1,6) which appears to give random results between 1 and 5. I thenuse this to select the colour number. 
 What we would like to do is weight the random results a bit to give say more of one colour. 
 For example: 
 colour 1 80% 
 colour 2 5% 
 colour 3 5% 
 colour 4 5% 
 colour 5 5% 
 another question would be how to set the seed so you could replicate or fix the outcome so it was repeatable. Maybe then connect this to a slider for testing options. 
 Thanks 
 Wayne

Mueller · Accepted Answer

This looks great. If you move SetRandomSeed( ) up outside of the loop in your function, then you'll get a consistent pattern.

Wayne Dickerson · Answer

Hi All, Just as a summary of where this got to. I have attached a DGN file with the script and a sample area of polygons (in an array) that I have randomly coloured with 5 different colours. This is then converted into solids by selecting by colour, this gave us 5 solid nodes (one for each colour) I changed the levelname for each of the solid nodes and then exported to a new DGN. We did this for a tile on a façade so we can apply a specific material in 5 variations. I can see however that you could use the random colour script to randomly colour a polygon façade breakup and then apply slightly different façade panels (via GNT) based on colours. To make it a bit more controllable I have locked the Random seed but also given variables to allow you to weight one colour over another. you can see this in the node inputs. Please note I haven't included any checks so you will have to make sure the values add up to 1 (100%). it still works if you break this rule but you will not get a spread of colours. If you would like any more info let me know. They 2 key scripts are included below. Thanks Wayne Random Polygon Script (with an offset for the tile joint) function (Polygon InputPoly, int RandomPool, double Ratio1, double Ratio2, double Ratio3, double Ratio4, double Ratio5, double TileOffSet) { Polygon TilePoly = {}; Point CentrePoint = {}; Polygon TilePolyArray = {}; int TileColour = 1; SetRandomSeed(5); for (int i = 0; i < InputPoly.Count; ++i) { Polygon TilePolylist= {}; for (int j = 0; j < InputPoly[i].Count; ++j) { int RNumber = Random(1,RandomPool); //select from the random numbers a weighted colour if(RNumber <= (RandomPool*Ratio1)) { TileColour = 1; } if(RNumber > (RandomPool*Ratio1) && RNumber <= (RandomPool*(Ratio1+Ratio2))) { TileColour = 2; } if(RNumber > (RandomPool*(Ratio1+Ratio2)) && RNumber <= (RandomPool*(Ratio1+Ratio2+Ratio3))) { TileColour = 3; } if(RNumber > (RandomPool*(Ratio1+Ratio2+Ratio3)) && RNumber <= (RandomPool*(Ratio1+Ratio2+Ratio3+Ratio4))) { TileColour = 4; } if(RNumber > (RandomPool*(Ratio1+Ratio2+Ratio3+Ratio4)) && RNumber <= (RandomPool*(Ratio1+Ratio2+Ratio3+Ratio4+Ratio5))) { TileColour = 5; } TilePoly = new Polygon(); CentrePoint = new Point(); CentrePoint.CentroidOfSet(InputPoly[i][j].Vertices); TilePoly.Offset(InputPoly[i][j],OffsetMethod.ByDistance,CentrePoint,TileOffSet); TilePoly.Color = TileColour; TilePolylist.Add(TilePoly); } TilePolyArray.Add(TilePolylist); } return TilePolyArray; } New Solid select by colour function (Polygon InputPoly, double SolidThickness, int RedValue, int GreenValue, int BlueValue) { Solid TileSolid = {}; Solid TileSolidArray = {}; for (int i = 0; i < InputPoly.Count; ++i) { Solid TileSolidList = {}; for (int j = 0; j < InputPoly[i].Count; ++j) { if (InputPoly[i][j].Color == color(r=RedValue,g=GreenValue,b=BlueValue)) { TileSolid = new Solid(); TileSolid.OffsetFromClosedCurve(InputPoly[i][j],SolidThickness,0); } else { TileSolid = {}; } TileSolidList.Add(TileSolid); } TileSolidArray.Add(TileSolidList); } return TileSolidArray; } 7380.GC_Tiles-small-test.dgn

Mueller · Answer

Hi Wayne, 
 That's a cool question. 
 What I would do in this case is to generate random numbers from 1 to 100 (for 100%). If the random number is from 1 to 80 then I'd assign color 1, 81 through 85 for color 2, etc. In some cases it may make sense to generate a larger range of random numbers and scale them to the target range in the model, e.g. 1 to 1000 and use 1 through 800 for color 1, etc. 
 Traditional random number generators are not truly random. The SetRandomSeed( N ) function can be used to make the random number results predictably reproducible. For each integer seed N the sequence of "randomly" generated numbers will be the same. This permits to create reproducible results while still allowing to vary the results by changing the random seed. Note that if the SetRandomSeed( N ) function call has no dependency to the rest of the GC model, a manual Update Model command may be required to see the effects of a changed seed N reflected in the geometry. If the seed N is set through a slider it may make sense to hook that slider up to some part of the model that will trigger an update of the affected geometry, even if that dependency's only purpose is to force the update and is otherwise ineffective --only indirectly via the random seed and the change in random number sequence. 
 I hope this makes sense. 
 Good success with your experiments! 
 Volker

Mueller · Answer

Hi Wayne, 
 In the function above you call SetRandomSeed( ) each time before calling Random( ). That will make Random( ) return the same number each time, because it'll reset the random sequence for each Random( ) call. SetRandomSeed( ) should be called only once for each full sequence of random numbers that is generated, for example at the start of a script, in any case before the first call to Random( ), then not until you want to start a new random sequence. 
 HTH, 
 Volker

Mueller · Answer

Hi Wayne, 
 In the conditional color is a type; therefore, color(1) is an unsupported expression. If you used color numbers in your polygon properties, then it will most likely work here to compare InputPoly[i][j].Color directly to that number, e.g. InputPoly[i][j].Color == 1. 
 As briefly discussed on the phone, move the declaration Solid TileSolidList = {}; into the outer loop, so that TileSolidList is reset for each iteration of the i-loop and accumulates only one full j-cycle before the next i-loop iteration clears out the list. 
 Regards, 
 Volker

Random with Weighted results

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