Hi, I am trying to dump the particle_positions to a file. Here is my extremely inefficient script... from yt.mods import * import pickle fn = "RedshiftOutput0000" # parameter file to load pf = load(fn) # load data all_data = pf.h.all_data() particle_positions_x = all_data['particle_position_x'] particle_positions_y = all_data['particle_position_y'] particle_positions_z = all_data['particle_position_z'] Dark_Matter_Density = all_data['Dark_Matter_Density'] # this is a Dataset {32, 32, 64} f1 = open('junk1', 'w') f2 = open('junk2', 'w') f3 = open('junk3', 'w') s1 = str(particle_positions_x) s2 = str(particle_positions_y) s3 = str(particle_positions_z) f1.write(s1) f2.write(s2) f3.write(s3) f1.close() f2.close() f3.close() How can I write out x-,y- and z positions in three columns in the same file ? And how to handle the array Dark_Matter_Density ? Shankar KU Cosmology