Factorio Forums

So, in case you have a design with multiple arbitrary items going down the same 4 lane bus, allow me to present a full-throughput compact filter using the new splitter mechanics.

[edited because as soon as I posted this I saw that it was using too many splitters and could be made simpler)
Capable of dealing with 4 full belts of what you want, 4 full belts of what you don't want, and any mix in between, without any stuttering or backing up of lanes.

I don't understand why you would need 6 splitters for 4 belts. You actually only need 4. One splitter for each input and two outputs.
Have a look at my design: Filter-/Excess Splitters

It uses only one splitter per belt. Of course my design is throughput limited because I merge some of the output belts, but you can easily change it to a throughput unlimited design by removing the merging splitters.

Yeah, that would be simpler! Oh well. I guess I went for the complicated answer first.

Remove the bottom most splitters. Move top row of splitters up one tile and add underground belts to the splitters before it for the unfiltered output. Put underground belts on the two middle lanes instead of the two lanes crossing. Saves you 2 needless splitters and is more compact.