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I just started using Mathematica. I got some output in a txt file from some computations in Pari/GP which looks like this:

$$ [1,2,3,4; 5,6,7,8]$$

Here I want to import the data into Mathematica and get a table. The semicolons indicate a new row and commas separate each entry on a row. I cannot figure out how to do this.

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2 Answers 2

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filename = "C:/data.txt";
First@ReadList[filename, Record, RecordSeparators -> {{"["}, {"]"}}] //
   StringSplit[#, ";"] & // 
 Map[Interpreter[DelimitedSequence["Number"]]]

{{1, 2, 3, 4}, {5, 6, 7, 8}}

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  • $\begingroup$ This works completely fine when the original matrix has dimensions like 3244 $\times$ 7. But for a row vector, as in the text file being [1,2,3,4], your code gives something like {{1,2,3,4}} with an extra brace, this is not interpreted as a matrix in Mathematica. $\endgroup$
    – Aditya Ghosh
    Commented Jul 25, 2023 at 12:32
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    $\begingroup$ @AdityaGhosh {{1,2,3,4}} is the Matrix in Mathematica. {{1, 2, 3, 4}} // MatrixQ is True. By the way, there not row vector or column vector in vector spaces. row or column only in Matrix. $\endgroup$
    – cvgmt
    Commented Jul 25, 2023 at 12:38
  • $\begingroup$ Evaluate: {Dimensions@#, MatrixQ@#} &@{{1, 2, 3, 4}}. Thanks for the comment by @cvgmt. $\endgroup$
    – Syed
    Commented Jul 25, 2023 at 12:38
  • $\begingroup$ I think using Catenate solves the issue for me, as it removes that extra brace $\endgroup$
    – Aditya Ghosh
    Commented Jul 25, 2023 at 12:40
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First we import the data as a string:

filename="d:/tmp/test.dat";
tmp=Import[filename][[1, 1]];

Then we adjust the syntax:

tmp= StringReplace[tmp , {"[" -> "{{", "]" -> "}}", ";" -> "},{"}]

Finally we convert the string into an expression and display it:

ToExpression[tmp] // TableForm

enter image description here

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  • $\begingroup$ Thanks, that solves it. But what's the utility of [[1, 1]] in the second line? $\endgroup$
    – Aditya Ghosh
    Commented Jul 25, 2023 at 11:44
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    $\begingroup$ This gets rid of unwanted braces. $\endgroup$
    – Daniel Huber
    Commented Jul 25, 2023 at 11:47
  • $\begingroup$ Actually, without [[1, 1]], I'm having this issue when I'm using this code on text like [0;1;2;3;4]. As you said, it's giving a lot of unwanted brackets. But including [[1, 1]] gives the errors: Part specification is longer than depth of object and String or list of strings expected at position 1 in StringReplace. Can you maybe explain how the argument [[1, 1]] works? $\endgroup$
    – Aditya Ghosh
    Commented Jul 25, 2023 at 12:04
  • $\begingroup$ Check what your file contains. test.dat contains: [1,2,3,4;5,6,7,8]. The import command should give a string like: {{"[1,2,3,4;5,6,7,8]"}} where the double quotes are not displayed by MMA. [[1,1,]] gets ride of the double braces. $\endgroup$
    – Daniel Huber
    Commented Jul 25, 2023 at 12:47

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