def get_particle_indices(cell_indices_strings, uniq_cell_indices_strings):
    """
    Returns a dicionary of lists of particle indices.

    Each key corresponds to one cell the list contains the indices of the particles this cell.
    This indices are used to retrieve the coordinates from the corresponding array (e.g., 'positions').
    """
    particle_indices = {}
    for k in uniq_cell_indices_strings:
        particle_indices[k] = []
    for i, k in enumerate(cell_indices_strings):
        particle_indices[k].append(i)
    return particle_indices