The → "Filter" daemon in RealFlow | Cinema 4D allows you to define simple comparisons and conditions, so-called expressions, in order to transfer particles between fluid containers.

Let's assume you want to filter the particles from “Fluid_A” against their velocities. If a particle' speed is lower than 2.0 the particle should be transferred to “Fluid_B”:

Target > Fluid_A
Source > Fluid_B
Condition > Expression
Under “Expression” enter: particle.speed < 2.0

You can use any other keywords from the table and modify the expression to your needs. It is also possible to combine expressions, e.g.

if particle.age > particle.velocity

Attribute	Expression keyword
Age	`particle.age, particle.isolation`
Collision	`particle.collision`
Density	`particle.density`
Force	`particle.force.mod, particle.force.x, particle.force.y, particle.force.z, particle.f.mod, particle.f.x, particle.f.y, particle.f.z`
ID	`particle.id`
Mass	`particle.mass`
Neighbors	`particle.nv, particle.neighbors, particle.neighbours`
Normal	`particle.normal.x, particle.normal.y, particle.normal.z`
Position	`particle.pos.x, particle.pos.y, particle.pos.z, particle.position.x, particle.position.y, particle.position.z`
Pressure	`particle.pressure`
Texture	`particle.texture.u, particle.texture.v, particle.texture.w`
Velocity	`particle.speed, particle.velocity.x, particle.velocity.y, particle.velocity.z, particle.vel.x, particle.vel.y, particle.vel.z`
Viscosity	`particle.viscosity`
Vorticity	`particle.vorticity.mod, particle.vorticity.x, particle.vorticity.y, particle.vorticity.z`
Emitter Id	`particle.emitterid*`

* An emitter's Id can be seen in the HUD.

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