How can I get rid of extra commas in Export/Import?

Question

Consider the following example of trying to export the following table:

Export["test.dat", {{{1, 1}, {2, 2}}, {{3, 3}, {4, 4}}}, "Table"];

Now I import to see what I get:

Import["test.dat", "Table"]
{{{1,,1}, {2,,2}}, {{3,, 3}, {4,,4}}}

which contains extra undesirable commas. I've trying making the data type a "List" but that possessing an issue in which elements are not separated by commas. How can I fix this problem so the the imported table is the same as I exported?

Answer 1

The problem is you are saving as text (you can see by looking at the FullForm of the Import[]). One way to fix it is to save to a .csv format, for instance

Export["test.csv", {{{1, 1}, {2, 2}}, {{3, 3}, {4, 4}}}]

Then you can import it back using

Import["test.csv"]

And you get the data you started with.

Answer 2

Another way:

Export["test.dat", {{{1, 1}, {2, 2}}, {{3, 3}, {4, 4}}}, "Table"];

Import["test.dat", "TSV"]

Answer 3

Another format especially suited for large amounts of multidimensional data is HDF (or also HDF5). It's overkill for your small example, but maybe you have larger sets in mind so that you could use this:

Export["test1.hdf", {{{1, 1}, {2, 2}}, {{3, 3}, {4, 4}}}];

Import["test1.hdf", {"Datasets", "Dataset1"}]

(* ==> {{{1, 1}, {2, 2}}, {{3, 3}, {4, 4}}} *)

Answer 4

To get something Mathematica will like, use

Export["test.m", {{{1, 1}, {2, 2}}, {{3, 3}, {4, 4}}}]

This will produce a file with the contents:

(* Created by Wolfram Mathematica 8.0 : www.wolfram.com *)
{{{1, 1}, {2, 2}}, {{3, 3}, {4, 4}}}