Why can't I import a file in the init.m file?

Question

I would like to have some data read in every time the kernel starts, but it doesn't seem to work. Say I have a CSV file I want to have read in, for example I use:

Export["/home/jason/temp.csv", Table[{n, 2 n, 3 n}, {n, 5}]];
Quit[];

Then I open up the init.m file in a text editor and add the line

temp123=Import["/home/jason/temp.csv"];

I save the file, then go back to a notebook and reopen the kernel and ask for the definition of temp123, it comes back as Null

?temp123

(*
 Global`temp123

 temp123=Null
*)

What is the best way to do this? I've tried putting the call to Import the CSV file in another file which is called by init.m, but the result is the same.

Thanks

Answer 1

I think that the reason is that -- depending on the format -- Import does either use external programs, java libraries via JLink or the frontend for imports of most "nontrivial" formats. Only some -- mainly simple ascii or plain binary -- formats and of course mathematicas own syntax are directly "imported" with pure kernel functionality. As you correctly suggested init.m is read early in the setup when the kernel not yet can make full use of all these features and thus it just isn't the right place to do that. Your own findings indicate that the setup of Import itself isn't even done before init.m is loaded. You should also note that Import is by definition a relatively slow operation (it often needs to start extra processes, load libraries, interact with the OS to read files and it furthermore tries to be smart about analyzing the file contents). Thus I would not suggest to make an import part of an init.m even if it would work, except you really enjoy the meditative tranquility when waiting for the kernel to start up :-).

What would be a relative simple way to achieve something that would provide functionality similar to what you want is to just predefine how to import the data you need in init.m, but defer the actual import to when the data is first used. This would typically be done at a later time when the kernel setup has finished and the import should work. You would just have to change the code in your init.m to:

temp123:=temp123=Import["/home/jason/temp.csv"];

init.m would then not be slowing down the startup process and the data would be imported on first use (and not at all if it isn't used in a particular session). Of course that'd fail if the data is already needed in the furhter code in init.m itself, then your current solution proposed in your own answer seems to be the best you can do. Another possibility would be to not use import but read the file as ascii text and parse the content with builtin string manipulation features which might be simple enough depending on the variability and complexity of your csv files...

Answer 2

For some reason I'm not aware of, Mathematica has trouble using the Import function when the kernel is first starting up. Perhaps it loads the init.m file before it loads the definitions of all the different file types. But apparently, it knows hot to Get from a properly formatted file. If I run

Export["/home/jason/temp.m", Table[{n, 2 n, 3 n}, {n, 5}]];
Quit[];

in a notebook, and then place this line in the init.m file

temp123=Get["/home/jason/temp.m"];

and then go back into the notebook, it has the desired effect:

?temp123

(*
 Global`temp123

 temp123={{1,2,3},{2,4,6},{3,6,9},{4,8,12},{5,10,15}}
*)

I'm not totally satisfied with this answer, but it does what I need it to do. I just have to convert the CSV files I have into .m files, and I can use them without having to call a package manually.