Import numeric data into Mathematica

Question

I have a C++ program that outputs a set of numbers at each time step. A blank line separates successive time steps. Here is an example of my data format:

0.2 42.8
0.4 12.3
0.6 32.1
0.8 37.3

0.2 44.2
0.4 17.8
0.6 39.0
0.8 30.1

I want to import this into Mathematica with the following format:

data = {
  {{0.2`, 42.8`}, {0.4`, 12.3`}, {0.6`, 32.1`}, {0.8`, 37.3`}},
  {{0.2`, 44.2`}, {0.4`, 17.8`}, {0.6`, 39.`},  {0.8`, 30.1`}}
  };

i.e., the data for each time step is in one list. How do I do this?

Answer 1

Assuming you mean you are writing the c++ program .. one approach (of many) to this is to directly write the file in mathematica form, that is simply put all the curly brackets and commas in the file.

You can then simply read it in with Get[].

This may seem a bit ugly, but with this approach you can readily handle cases where you might have variable length data in each time series.

If you just write the raw numbers to the file and use ReadList[] you'll need to tell mathematica how to partition the data.

Edit: approach based on verbia's comment:

Assuming you have a file like this:

1 2
2 4
5 6
<blank>
1 3
5 9
8 3
9 10
<blank>

You can read in the form requested as :

ReadList[filename, {Number, Number},
      RecordLists -> True,
      RecordSeparators -> {"\n\n"}]

Quite simple and avoids the need to specify the lenght of each record a priori.

Answer 2

edited with updated file format

DeleteCases[SplitBy[ImportString["0.2 42.8
     0.4 12.3
     0.6 32.1
     0.8 37.3 

     0.2 44.2
     0.4 17.8
     0.6 39.0
     0.8 30.1", "Table"], # == {} &], {{}}]

{{{0.2, 42.8}, {0.4, 12.3}, {0.6, 32.1}, {0.8, 37.3}}, {{0.2, 44.2}, {0.4, 17.8}, {0.6, 39.}, {0.8, 30.1}}}