Thank you so much for your reply. To give specifics of my files and what I want to do, I am doing simulations with dark matter haloes from redshift 30 to 20 and trying to track the haloes with mass > 10^6 Msun. My simulation generates catalogs at a given redshift (Z), from Z= 30 to 20 with a redshift jump of 0.1. Each of these catalogs (in .dat) are named with their redshift and contains halo ID (a unique 7 digit number to specify each halo), their position (x,y,z), so there are in total 4 columns.
With Mathematica, I want to make three plots Z vs x, Z vs y and Z vs z to track the history of each halo since the time they were born. I know about the import option, and also the chart bubble option (which might help in designating a specific colored bubble for each halo, so that we may identify them).
My idea so far is to add a fifth column in the data files with redshift, and then import column 4 (halo ID) as a list to a variable "i", such that i1, i2, i_3 .... are the first halo id, the second halo id and so on. Then to import the coordinates as usual and then to use bubble chart option based on the variable "i" to plot redshift vs x and redshift vs y and so on..