Skip to main content

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


Comments

Popular posts from this blog

front end - keyboard shortcut to invoke Insert new matrix

I frequently need to type in some matrices, and the menu command Insert > Table/Matrix > New... allows matrices with lines drawn between columns and rows, which is very helpful. I would like to make a keyboard shortcut for it, but cannot find the relevant frontend token command (4209405) for it. Since the FullForm[] and InputForm[] of matrices with lines drawn between rows and columns is the same as those without lines, it's hard to do this via 3rd party system-wide text expanders (e.g. autohotkey or atext on mac). How does one assign a keyboard shortcut for the menu item Insert > Table/Matrix > New... , preferably using only mathematica? Thanks! Answer In the MenuSetup.tr (for linux located in the $InstallationDirectory/SystemFiles/FrontEnd/TextResources/X/ directory), I changed the line MenuItem["&New...", "CreateGridBoxDialog"] to read MenuItem["&New...", "CreateGridBoxDialog", MenuKey["m", Modifiers-...

How to thread a list

I have data in format data = {{a1, a2}, {b1, b2}, {c1, c2}, {d1, d2}} Tableform: I want to thread it to : tdata = {{{a1, b1}, {a2, b2}}, {{a1, c1}, {a2, c2}}, {{a1, d1}, {a2, d2}}} Tableform: And I would like to do better then pseudofunction[n_] := Transpose[{data2[[1]], data2[[n]]}]; SetAttributes[pseudofunction, Listable]; Range[2, 4] // pseudofunction Here is my benchmark data, where data3 is normal sample of real data. data3 = Drop[ExcelWorkBook[[Column1 ;; Column4]], None, 1]; data2 = {a #, b #, c #, d #} & /@ Range[1, 10^5]; data = RandomReal[{0, 1}, {10^6, 4}]; Here is my benchmark code kptnw[list_] := Transpose[{Table[First@#, {Length@# - 1}], Rest@#}, {3, 1, 2}] &@list kptnw2[list_] := Transpose[{ConstantArray[First@#, Length@# - 1], Rest@#}, {3, 1, 2}] &@list OleksandrR[list_] := Flatten[Outer[List, List@First[list], Rest[list], 1], {{2}, {1, 4}}] paradox2[list_] := Partition[Riffle[list[[1]], #], 2] & /@ Drop[list, 1] RM[list_] := FoldList[Transpose[{First@li...

plotting - Magnifying Glass on a Plot

Although there is a trick in TEX magnifying glass but I want to know is there any function to magnifying glass on a plot with Mathematica ? For example for a function as Sin[x] and at x=Pi/6 Below, this is just a picture desired from the cited site. the image got huge unfortunately I don't know how can I change the size of an image here! Answer Insetting a magnified part of the original Plot A) by adding a new Plot of the specified range xPos = Pi/6; range = 0.2; f = Sin; xyMinMax = {{xPos - range, xPos + range}, {f[xPos] - range*GoldenRatio^-1, f[xPos] + range*GoldenRatio^-1}}; Plot[f[x], {x, 0, 5}, Epilog -> {Transparent, EdgeForm[Thick], Rectangle[Sequence @@ Transpose[xyMinMax]], Inset[Plot[f[x], {x, xPos - range, xPos + range}, Frame -> True, Axes -> False, PlotRange -> xyMinMax, ImageSize -> 270], {4., 0.5}]}, ImageSize -> 700] B) by adding a new Plot within a Circle mf = RegionMember[Disk[{xPos, f[xPos]}, {range, range/GoldenRatio}]] Show...