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Capture, Reuse 85A backreference in TextWrangler’s Find and ReplaceFixing misshapen dates is one of my most common daily uses for regexes. Dates usually contain anobvious pattern, e.g. 9/5/2010 and 4-7-99. To get them into a different format – e.g. 9/5/10 and04/07/1999 – can often be accomplished with regex techniques.Exercise: Change the order of date partsIn American day-to-day usage, dates are often formatted as month-day-year:03-09-200111-14-201205-22-1978However, programmers prefer dates to be in year-month-day format:2001-03-092012-11-141978-05-22Why? A common operation is to “find the earliest/latest date.” To sort date strings, thesimplest method for a program is to do it an alphabetical-fashion. Think of how you sort wordsalphabetically:
Capture, Reuse 86ApplesOraclesOrangesOreThe most important letter is the left-most one: A comes before O in the alphabet, so all words thatbegin with A will come before any word that starts with O. But what if the words start with the sameletter? Then you compare the second letters, and so forth.This is the same with dates. In the American human-readable format, 03-09-2001 would comebefore 05-22-1978, as 03 comes earlier in the numerical scale than does 05. But chronologically, ofcourse, 05-22-1978 is several decades before 03-09-2001. In the programmer-friendly version, the“biggest” parts of the date come first, i.e. the year, then the month and day. This makes sorting easy,because the alphabetical-order of the date text is the same as the chronological order of the actualdates.So, given the human readable version of the dates, write a regex that converts them to theprogrammer friendly version.AnswerFind (\d+)-(\d+)-(\d+)Replace $3-$1-$2Exercise: Zero-pad the datesThe above exercise isn’t completely realistic, however, because the human-readable dates are usuallywritten in a more shorthand way:3-9-200111-14-20125-22-1978The month of March, in other words, is written simply as 3, not as 03Why is that extra zero there? If you think of the computer-sortable scenario, those extra zeros arevital. Consider the issue of two dates with the same year. In human readable format:11-20-20023-20-2002In machine-readable format:
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The Bastards Book ofRegular Express
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CONTENTSOptionality and alternation
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CONTENTSSwitching visualizations (T
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Regular Expressions are for Everyon
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Regular Expressions are for Everyon
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Getting Started6
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Finding a proper text editor 8Notep
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Finding a proper text editor 10Edit
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Finding a proper text editor 12Text
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Finding a proper text editor 14does
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Finding a proper text editor 16Yest
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Finding a proper text editor 18A do
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A better Find-and-Replace 20The lim
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A better Find-and-Replace 22Using R
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Your first regex 24helloThe Find-an
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Your first regex 26The regex syntax
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Your first regex 28Double-bounded
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Your first regex 30AnswerFind \bcat
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Removing emptinessIt’s funny how
Page 41 and 42: Removing emptiness 34Now let’s do
Page 43 and 44: Removing emptiness 36…as opposed
Page 45 and 46: Removing emptiness 38Replacement in
Page 47 and 48: Match one-or-more with the plus sig
Page 55 and 56: Match zero-or-more with the star si
Page 57 and 58: Specific and limited repetition 501
Page 59 and 60: Specific and limited repetition 52E
Page 61 and 62: Specific and limited repetition 54C
Page 63 and 64: Anchors: A way to trim emptinessIn
Page 65 and 66: Anchors: A way to trim emptiness 58
Page 71 and 72: Matching any letter, any number 64A
Page 73 and 74: Matching any letter, any number 66W
Page 75 and 76: Matching any letter, any number 68[
Page 77 and 78: Matching any letter, any number 70R
Page 79 and 80: Matching any letter, any number 72F
Page 81 and 82: Matching any letter, any number 74A
Page 83 and 84: Negative character sets 76$1,200.00
Page 85 and 86: Negative character sets 78\W+Exerci
Page 87 and 88: Capture, Reuse 80Find (ba)+Matches
Page 89 and 90: Capture, Reuse 82.- then the 1st ba
Page 91: Capture, Reuse 84In English We are
Page 95 and 96: Capture, Reuse 8805-14-8912-03-9803
Page 97 and 98: Capture, Reuse 90Mary asked: "What
Page 99 and 100: Optionality and alternationThe two
Page 101 and 102: Optionality and alternation 94Answe
Page 103 and 104: Optionality and alternation 96Studi
Page 105 and 106: Optionality and alternation 98You m
Page 107 and 108: Laziness and greediness 100Being to
Page 109 and 110: Laziness and greediness 102Replace
Page 111 and 112: Laziness and greediness 104With the
Page 113 and 114: Lookarounds 106cat(?=s)- will match
Page 115 and 116: Lookarounds 108`(?
Page 117 and 118: Lookarounds 110ExerciseGiven the fo
Page 119 and 120: Lookarounds 112City,CountryAlbuquer
Page 121 and 122: Lookarounds 114Given this list of c
Page 123 and 124: Lookarounds 116100,J.D. Salinger Av
Page 125 and 126: Lookarounds 1186,300|Apples|New Yor
Page 127 and 128: Lookarounds 120^(\d+) Record ID (\w
Page 129 and 130: Lookarounds 122d. Remove all asides
Page 131 and 132: From Data to HTML (TODO)This chapte
Page 133 and 134: From Data to HTML (TODO) 126Turning
Page 135 and 136: The ExercisesI’ve never been one
Page 137 and 138: Data Cleaning with the Stars 130LOR
Page 139 and 140: Data Cleaning with the Stars 132[GM
Page 141 and 142: Finding needles in haystacks (TODO)
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Changing phone format (TODO)Todo: T
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Changing phone format (TODO) 138Exe
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Changing phone format (TODO) 140Ans
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Changing phone format (TODO) 142`1-
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Changing phone format (TODO) 144(\d
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Dating, Associated Press Style (TOD
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Sorting a police blotter 154Sloppy
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Sorting a police blotter 156I used
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Converting XML to tab-delimited dat
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Converting XML to tab-delimited dat
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Cleaning up Microsoft Word HTML(TOD
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Cleaning up OCR Text (TODO)Image sc
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Moving forwardThank you for taking
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