# Combine particle sets

This modifier loads a set of particles from a second file and merges them into the current dataset.

Note: The simulation cell loaded from the second file is ignored. The modifier does not change the current simulation box. Use e.g. the Affine transformation modifier in case you need to expand the simulation cell to accommodate all particles.

If both the primary and the secondary data sources contain multiple simulation frames, then the modifier combines corresponding frames from each source. For the second data source, you may have to explicitly specify a wildcard filename pattern or check the "File contains time series" option to let OVITO load more than just the first frame of the simulation sequence.

The IDs of particles loaded from the second file are newly assigned by the modifier to ensure that they do not conflict with the existing particle IDs in the current dataset.