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Re: Input, output troubles me ...


luigirmailbox-mathematica at yahoo.it wrote:
> Dear Friends
> 
> I have been using Mathematica for text file processing for a long time.
> I found it's a valuable tool for text complex manipulations.
> 
> The strategy I was used to apply is well condensed in this childish
> example:
> 
> ---------------------------------
> (*loading the content*)
> dummy = Import["c:\\myDir\\inputFile.txt", "Lines"];
> (*processing it*)
> dummy = Select[dummy, (# != "a") &];
> (*exporting it*)
> Export["c:\\myDir\\outpuFile.txt", dummy, "Lines"];
> ---------------------------------
> 
> Now I have to face huge file (up to 5,6 Gb sized) and the previous
> technique mostly crashes my systems.
> 
> I would like to process a single line, rather than the whole load,
> doing something similar what a classical programmig language does:
> 
> ---------------------------------
> Open "c:\\myDir\\inputFile.txt" for Input As #1
> Open "c:\\myDir\\outputFile.txt" for Input As #2
> 
> Do While Not Eof(#1)
>    Line Input #1, dummy$
>    If dummy$ <> "a" Then Print #1, dummy$
> Loop
> 
> Close #1
> Close #2
> ---------------------------------
> 
> I tried this (and many others!) trick:
> 
> ---------------------------------
> stream1 = OpenRead["c:\\myDir\\inputFile.txt"];
> stream2 = OpenWrite["c:\\myDir\\outputFile.txt"];
> While[
>    dummy != EndOfFile,
>    dummy = Read[stream1, "String"];
>    If[dummy != "a", Write[stream2, dummy]];
> ]
> Close[stream1];
> Close[stream2];
> ---------------------------------
> 
> But it doesn't work: when inputFile is
> 
> a
> b
> c
> d
> 
> outputFile is void, not
> 
> b
> c
> d
> 
> as expected.
> 
> Plaese can someone help me?
> 
> Thanks for your attention.
> Goobye.
> 

Two things:

. The variable dummy must be initialize to something before entering the 
loop.

. Use UnsameQ (shorthand =!= ) rather than not equal to test the end of 
file.

stream1 = OpenRead["c:\\temp\\inputFile.txt"];
stream2 = OpenWrite["c:\\temp\\outputFile.txt"];

dummy = Read[stream1, "String"];

While[dummy =!= EndOfFile,
   If[dummy != "a", Write[stream2, dummy]];
    dummy = Read[stream1, "String"]; ]

Close[stream1];
Close[stream2];

Regards,
Jean-Marc


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