Exporting tabulated data into an ASCII file preserving column alignment

Question

I have some problems exporting Table data into ASCII files preserving column alignment.

By example (under Mathematica v11.2 + Linux):

I generate a random table with 2 columns

t = Table[StringJoin[RandomChoice[CharacterRange["A", "Z"], RandomInteger[{1,10}]]], 10, 2];

UOTKRPUOVS   PZFON
WQSMI        FVAGV
SGOZQJP      KYWTGIBGF
B            QEKUEFN
EKPU         WVIKS
CHXJBPGXA    BAMYNNG
FZFXXWZ      TQUYN
A            K
ICZFK        MDLKDKIGTD
NLXH         WVAWTL

I export it into a Text file with this command:

Export["test.txt", t, "Table"]

However if I look the exported file (from terminal):

cat test.txt

I get:

UOTKRPUOVS    PZFON
WQSMI FVAGV
SGOZQJP   KYWTGIBGF
B QEKUEFN
EKPU  WVIKS
CHXJBPGXA BAMYNNG
FZFXXWZ   TQUYN
A K
ICZFK MDLKDKIGTD
NLXH  WVAWTL

-> column alignment is completely lost.

Fix?:

The only way I have found so far to fix this issue is to export the table using:

Export["test.txt", StringReplace[ToString[Grid[t]], "\n\n" -> "\n"], "Text"]

Now,

cat test.txt

gives me back the right formatting:

UOTKRPUOVS   PZFON
WQSMI        FVAGV
SGOZQJP      KYWTGIBGF
B            QEKUEFN
EKPU         WVIKS
CHXJBPGXA    BAMYNNG
FZFXXWZ      TQUYN
A            K
ICZFK        MDLKDKIGTD
NLXH         W

This works but that seems a very awkward solution for such a basic problem...

Any better idea?

---

Note: maybe the StringReplace[..., "\n\n" -> "\n"] step is useless under Windows, but I had not the opportunity to check that.

Answer 1

You can do :

t = Table[StringJoin[RandomChoice[CharacterRange["A", "Z"], RandomInteger[{1, 10}]]],10, 2];  

ToString@Format[TableForm[t, TableSpacing -> {0, 1}], OutputForm]

Then export the string.

Surpisingly it works fine too with arbitrary ragged nested list :

    ToString@Format[
  TableForm[{12, s, {2, 6777}, {6, 8, {7, 8}}}, 
   TableSpacing -> {0, 1}, TableAlignments -> {Left, Top, Left}], 
  OutputForm] 

This functionality of Mathematica is very old. (Mma 2 at least). It may be supersed by something more modern.

EDIT

It is also possible to write directly in a file, like this :

st = OpenWrite["test.txt", FormatType ->  OutputForm];
Write[st, TableForm[t, TableSpacing -> {0,1}]];
Close[st];
Import["test.txt"]

(* same output as above *)

Answer 2

Slight modifications of the code in the question:

t = Table[StringJoin[RandomChoice[CharacterRange["A", "Z"], RandomInteger[{1, 10}]]], 10, 4];
Export[FileNameJoin[{NotebookDirectory[], "test.txt"}], t, "Table"];
RunProcess[{"cat", FileNameJoin[{NotebookDirectory[], "test.txt"}]}]["StandardOutput"]

The following export code might be too ad hoc but works:

Clear[AddSpaces]
AddSpaces[col : {_String ..}] :=
  Block[{m = Max@Map[StringLength, col]},
   Map[StringJoin[#, StringJoin @@ Table[" ", m - StringLength[#]]] &,
     col]
   ];

t2 = Transpose[Map[AddSpaces, Transpose[t]]];
Export[FileNameJoin[{NotebookDirectory[], "test2.txt"}], t2, "Table"];

RunProcess[{"cat" , FileNameJoin[{NotebookDirectory[], "test2.txt"}]}]["StandardOutput"]

(I strongly suspect there is a solution using the options of Export.)