Deleting lines that repeat the first 15 characters



  • Hello, @mangoguy, @scott-sumner and All,

    I’m extremely confused, Indeed ! I did an important and beginner mistake, in my previous regex, that I was testing, intensively :-(( My God, of course ! The RIGHT regex is (?-s)^(.{15}).*\R\K(?:\1.*\R)+ and NOT the regex (?-s)(.{15}).*\R\K(?:\1.*\R)+ :-))

    Do you see the difference ? Well, it’s just the anchor ^, after the modifier (?-s) !

    Indeed, let’s try again the wrong regex :

    Assuming the test list, below :

    91,02,2013,1000   000001   ,22.107,22.513,20.976,21.151,0
    13,1000   000002   ,20.976,21.724,20.620,21.336,0
    13,1000   000003   ,21.344,22.116,21.336,21.918,0
    13,1000   000004   ,21.918,21.918,20.797,20.797,0
    

    So, first, the caret is right before the 9 digit, of the first line and the fifteen characters 91,02,2013,1000 cannot be found elsewhere. Then, as no anchor ^ ( beginning of line ) exists, the regex engine goes ahead one position between the digits 9 and 1 of the first line. Again, as the fifteen characters 1,02,2013,1000b do not exist further on, the regex engine goes ahead one position, examining, now the string ,02,2013,1000bb

    … till the fifteen characters 13,1000bbb00000, which can be found, this time, at beginning of lines 2, 3 and 4 ! Just imagine the work to accomplish for 458,404 lines of the Data2.txt file :-((

    ( Note : the lowercase letter b, above, stands for a space character )

    To easily see the problem, just get rid of the \K syntax, forming the regex (?-s)(.{15}).*\R(?:\1.*\R)+. If you click on the Find Next button, it selects, after test on positions 1, 2,…and 8, from the two last digits of year 2013 till the end of text. But, if you’re using the regex (?-s)^(.{15}).*\R(?:\1.*\R)+, with the anchor ^, it correctly gets the identical lines 2, 3 and 4, regarding theirs first 15 characters !


    So, Doug, to sump up, using the right regex (?-s)^(.{15}).*\R\K(?:\1.*\R)+, against your Data2.txt file, does not find any occurrence ( ~5s ), that is the expected result, as we know, by construction, that the 458,404 lines of this file, are all different :-)

    Best Regards,

    guy038



  • @guy038

    Yea, wow, I totally didn’t see the missing ^ as well. Of course, as our local regex guru I don’t normally question @guy038’s regexes, but there is no excuse for a second pair of eyes (mine) not noticing/questioning this. Looking back over my posts in this thread, I really added nothing of value and totally wish I hadn’t participated at all. :-(


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