A Filter is a Physlet that takes data from a data source, processes the data, and passes this processed data to a data listener.
This test page contains two data sources and four data filters. The red and the green particles each send a state datum (e.g., a state datum for a particle in the Molecular package contains the variables t, x, y, vx, vy, m) to their data listeners at every clock tick. The Histogram data listeners sort this data into bins while the Accumulator data listeners store this data in a data set. The bin-ed data and the stored data are then passed on to DataGraphs for display.
See the Accumulator and Histogram documentation and sample scripts for more complete information about these data filters.