Probability Sampling

Menu Path : Operator > Logic > Probability Sampling

The Probability Sampling Operator performs a kind of switch/case operation where a weight controls the probability of selecting a case. If all weights are equal, this Operator produces a uniform distribution of the different output values.

Operator settings

Setting	Description
Integrated Random	(Inspector) Specifies whether this Operator generates the random number itself, or if it allows you to input a custom random number instead.
Seed	Defines the scope of the random number. For more information, see Random Number. This setting only appears if you enable Integrated Random.
Constant	Specifies whether the generated random number is constant or not. For more information, see Random Number. This setting only appears if you enable Integrated Random.
Entry Count	The number of cases to test. The maximum value is 32.

Operator properties

Input	Type	Description
Weight 0	float	The weight for the first value. The larger this value is compared to the rest of the weights, the higher the chance the Operator selects the first value.
Value 0	Configurable	The value to output if the Operator selects Weight 0.
Weight 1	float	The weight for the second value. The larger this value is compared to the rest of the weights, the higher the chance the Operator selects the second value.
Value 1	Configurable	The value to output if the Operator selects Weight 1.
Weight N	float	To expose more cases, increase the Entry Count.
Value N	Configurable	To expose more cases, increase the Entry Count.
Rand	float	The value this Operator uses to choose a value from amongst the weights. This should be between 0 and 1.This property only appears if you disable Integrated Random.
Hash	uint	The value this Operator uses to create a constant random value. This property only appears if you enable Constant.

Output	Type	Description
Output	Configurable	The value where the corresponding case entry is equal to Input value or, if there isn’t any match, Default.

Operator configuration

To view the Node's configuration, click the cog icon in the Node's header.

Property	Description
Type	The value type this Operator uses. For the list of types this property supports, see Available types.

Available types

You can use the following types for your Input values and Output ports:

• Bool
• Int
• Uint
• Float
• Vector2
• Vector3
• Vector4
• Gradient
• AnimationCurve
• Matrix
• OrientedBox
• Color
• Direction
• Position
• Vector
• Transform
• Circle
• ArcCircle
• Sphere
• ArcSphere
• AABox
• Plane
• Cylinder
• Cone
• ArcCone
• Torus
• ArcTorus
• Line
• Flipbook
• Camera

This list does not include any type that corresponds to a buffer or texture because it is not possible to assign these types as local variables in generated HLSL code.

Details

The internal algorithm of this Operator can be described by this sample code :

//Input

float[] weight = { 0.2f, 1.2f, 0.7f };

char[] values = { 'a', 'b', 'c' };

//Compute prefix sum of height

float[] prefixSumOfWeight = new float[height.Length];

prefixSumOfHeight[0] = weight[0];

for (int i = 1; i < weight.Length; ++i)

    prefixSumOfHeight[i] = weight[i] + weight[i - 1];

//Pick a random value [0, sum of all height]

var rand = Random.Range(0.0f, weight[weight.Length - 1]);

//Evaluate probability sampling

char r = 'z';

for (int i = 0; i < weight.Length; ++i)

{

    if (rand < prefixSumOfWeight[i] || i == weight.Length - 1)

    {

        r = values[i];

        break;

    }

}

//Output

Debug.Log("Result : " + r.ToString());