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text - Skip header lines on import


When importing a data file what are the comment symbols for Mathematica? That is, given a file like this


blabla
bulbul


1 2 6 54 7 ...
..

what symbol do I have to put in front of header lines so Mathematica skips them and starts reading at the line 1 2 6 54 7 .... I tried #, which works in gnuplot, but that did not work.


I know that I could just tell Mathematica to skip the lines, but as I can control the file output, it would be nicer to use some kind of a tag.



Answer



Here is an approach that handles interspersed comments in addition to "headers"


 FilePrint["test.txt"]



#comment
#comment
#comment
1 2 3
#c2
4 5 6
7 8 9

 ImportString[

     StringReplace[Import["test.txt", "Text"], 
         StartOfLine ~~ "#" ~~ Shortest[___] ~~ EndOfLine ~~ "\n" -> ""], "Table"]


{{1, 2, 3}, {4, 5, 6}, {7, 8, 9}}



of course you can invent whatever convention you want or even a mix, eg..


 `StartOfLine ~~ {"#", "!", "%"} ~~ ...`

another variant:



 ImportString[StringJoin@Riffle[
      Select[StringSplit[Import["test.txt", "Text"], "\n"],
            StringTake[#, 1] != "#" &], "\n"], "Table"]

Even handle end-of-line comments:



#comment
1 2 3
#c2
4 5 6  #note 1

7 8 9  

 ImportString[StringReplace[Import["test.txt", "Text"], {
      StartOfLine ~~ "#" ~~ Shortest[___] ~~ EndOfLine ~~ "\n" -> "",
                     "#" ~~ Shortest[___] ~~ EndOfLine -> ""
                                       }], "Table"]


{{1, 2, 3}, {4, 5, 6}, {7, 8, 9}}




Tested on Windows by the way -- this might need some tweaking to handle different line endings on other systems


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