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  • Why is negation of a regex needed?

    - by Lazer
    There are so many questions on regex-negation here on SO. I am not sure I understand why people feel the need to negate a regex. Why not use something like grep -v that shows only the results that do not match the regex? $ ls april august december february january july june march may november october september $ ls | grep ber december november october september $ ls | grep -v ber april august february january july june march may

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  • Lucene's nested query evaluation regarding negation

    - by ponzao
    Hi, I am adding Apache Lucene support to Querydsl (which offers type-safe queries for Java) and I am having problems understanding how Lucene evaluates queries especially regarding negation in nested queries. For instance the following two queries in my opinion are semantically the same, but only the first one returns results. +year:1990 -title:"Jurassic Park" +year:1990 +(-title:"Jurassic Park") The simplified object tree in the second example is shown below. query : Query clauses : ArrayList [0] : BooleanClause "MUST" occur : BooleanClause.Occur "year:1990" query : TermQuery [1] : BooleanClause "MUST" occur : BooleanClause.Occur query : BooleanQuery clauses : ArrayList [0] : BooleanClause "MUST_NOT" occur : BooleanClause.Occur "title:"Jurassic Park"" query : TermQuery Lucene's own QueryParser seems to evaluate "AND (NOT" into the same kind of object trees. Is this a bug in Lucene or have I misunderstood Lucene's query evaluation? I am happy to give more information if necessary.

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  • Double Negation in C++ code.

    - by Brian Gianforcaro
    I just came onto a project with a pretty huge code base. I'm mostly dealing with C++ and a lot of the code they write uses double negation for their boolean logic. if (!!variable && (!!api.lookup("some-string"))) { do_some_stuff(); } I know these guys are intelligent programmers, it's obvious they aren't doing this by accident. I'm no seasoned C++ expert, my only guess at why they are doing this is that they want to make absolutely positive that the value being evaluated is the actual boolean representation. So they negate it, then negate that again to get it back to its actual boolean value. Is this a correct? or am I missing something else? Thanks, Brian Gianforcaro

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  • Manipulating matrix operations (transpose, negation, addition, and mutiplication) using functions in

    - by user292489
    I was trying to manipulate matrices in my input file using functions. My input file is: A 3 3 1 2 3 4 5 6 7 8 9 B 3 3 1 0 0 0 1 0 0 0 1 C 2 3 3 5 8 -1 -2 -3 D 3 5 0 0 0 1 0 1 0 1 0 1 0 1 0 0 1 E 1 1 10 F 3 10 1 0 2 0 3 0 4 0 5 0 0 2 3 -1 -3 -4 -3 8 3 7 0 0 0 4 6 5 8 2 -1 10 I am having trouble in implementing the functions that I declared. I assumed my program will perform those operations: transpose, negate, add, and multiply matices according to the users choice: /* once this program is compiled and executed, it will perform the basic matrix * operations: negation, transpose, addition, and multiplication. */ #include <stdio.h> #include <stdlib.h> #define MAX 10 int readmatrix(FILE *input, char martixname[6],int , mat[10][10], int i, int j); void printmatrix(char matrixname[6], int mat[10][10], int i, int j); void Negate(char matrixname[6], int mat[10][10], int i, int j); void add(char matrixname[6], int mat[10][10],int i, int k); void multiply(char matrixname[], int mat[][10], char A[], int i, int k); void transpose (char matrixname[], int mat[][10], char A[], int); void printT(int mat[][10], int); int selctoption(); char selectmatrix(); int main(int argc, char *argv[]) { char matrixtype[6]; int mat[][10]; FILE *filein; int size; int optionop; int matrixop; int option; if (argc != 2) { printf("Usage: executable input.\n"); exit(0); } filein = fopen(argv[1], "r"); if (!filein) { printf("ERROR: input file not found.\n"); exit (0); } size = readmatrix (filein, matrixtype); printmatrix(matrix[][10], size); option = selectoption(); matrixtype = selectmatrix(); //printf("You have: %5.2f ", deposit); optionop = readmatrix(option, matrix[][10], size); if (choiceop == 6) { printf("Thanks for using the matrix operation program.\n"); exit(0); } printf("Please select from the following matrix operations:\n") printf("\t1. Print matrix\n"); printf("\t2. Negate matrix\n"); printf("\t3. Transpose matrix\n"); printf("\t4. Add matrices\n"); printf("\t5. Multiply matrices\n"); printf("\t6. Quit\n"); fclose(filein); return 0; } do { printf("Please select option(1-%d):", optionop); scanf("%d", &matrixop); } while(matrixop <= 0 || matrixop > optionop); void readmatrix (FILE *in, int mat[][10], char A[], int i, int j) { int i=0,j = 0; while (fscanf(in, "%d", &mat[i][j]) != EOF) return 0; } // I would appreciate anyone's feedback.

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  • manuplating matrix operation(transpose, negation, addition, and mutipication) using functions in c

    - by user292489
    i was trying to manuplate matrices in my input file using functions. my input file is, A 3 3 1 2 3 4 5 6 7 8 9 B 3 3 1 0 0 0 1 0 0 0 1 C 2 3 3 5 8 -1 -2 -3 D 3 5 0 0 0 1 0 1 0 1 0 1 0 1 0 0 1 E 1 1 10 F 3 10 1 0 2 0 3 0 4 0 5 0 0 2 3 -1 -3 -4 -3 8 3 7 0 0 0 4 6 5 8 2 -1 10 i am having trouble in impementing the funcitons that i declared. i assumed my program will perform those operations: transpose, negate, add, and mutiply matices according to the users choise: /* once this program is compliled and excuted, it will perform the basic matrix operations: negation, transpose,a\ ddition, and multiplication. */ #include <stdio.h> #include <stdlib.h> #define MAX 10 int readmatrix(FILE *input, char martixname[6],int , mat[10][10], int i, int j); void printmatrix(char matrixname[6], int mat[10][10], int i, int j); void Negate(char matrixname[6], int mat[10][10], int i, int j); void add(char matrixname[6], int mat[10][10],int i, int k); void multiply(char matrixname[], int mat[][10], char A[], int i, int k); void transpose (char matrixname[], int mat[][10], char A[], int); void printT(int mat[][10], int); int selctoption(); char selectmatrix(); int main(int argc, char *argv[]) { char matrixtype[6]; int mat[][10]; FILE *filein; int size; int optionop; int matrixop; int option; if (argc != 2) { printf("Usage: excutable input.\n"); exit (0); } filein = fopen(argv[1], "r"); if (!filein) { printf("ERROR: input file not found.\n"); exit (0); } size = readmatrix (filein, matrixtype); printmatrix(matrix[][10], size); option = selectoption(); matrixtype = selectmatrix(); //printf("You have: %5.2f ", deposit); optionop = readmatrix(option, matrix[][10], size); if (choiceop == 6) { printf("Thanks for using the matrix operation program.\n"); exit(0); } printf("Please select from the following matrix operations:\n") printf("\t1. Print matrix\n"); printf("\t2. Negate matrix\n"); printf("\t3. Transpose matrix\n"); printf("\t4. Add matrices\n"); printf("\t5. Multiply matrices\n"); printf("\t6. Quit\n"); fclose(filein); return 0; } do { printf("Please select option(1-%d):", optionop); scanf("%d", &matrixop); }while(matrixop <= 0 || matrixop > optionop); void readmatrix (FILE *in, int mat[][10], char A[], int i, int j) { int i=0,j = 0; while (fscanf(in, "%d", &mat[i][j]) != EOF) return 0; } // i would apprtaite anyones feedback. //thank you!

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  • Algorithm for Negating Sentences

    - by Kevin Dolan
    I was wondering if anyone was familiar with any attempts at algorithmic sentence negation. For example, given a sentence like "This book is good" provide any number of alternative sentences meaning the opposite like "This book is not good" or even "This book is bad". Obviously, accomplishing this with a high degree of accuracy would probably be beyond the scope of current NLP, but I'm sure there has been some work on the subject. If anybody knows of any work, care to point me to some papers?

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  • Regex to match a whole string only if it lacks a given substring/suffix

    - by Ivan Krechetov
    I've searched for questions like this, but all the cases I found were solved in a problem-specific manner, like using !g in vi to negate the regex matches, or matching other things, without a regex negation. Thus, I'm interested in a “pure” solution to this: Having a set of strings I need to filter them with a regular expression matcher so that it only leaves (matches) the strings lacking a given substring. For example, filtering out "Foo" in: Boo Foo Bar FooBar BooFooBar Baz Would result in: Boo Bar Baz I tried constructing it with negative look aheads/behinds (?!regex)/(?<!regex), but couldn't figure it out. Is that even possible?

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  • How to negate the whole regex?

    - by 01
    I have a regex, for example ([m]{2}|(t){1}). It matches ma and t and doesn't match bla. I want to negate the regex, thus it must match bla and not ma and t, by adding something to this regex. I know I can write bla, the actual regex is however more complex.

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  • how to negate whole regex ??

    - by 01
    I have regex (for example) ([m]{2}|(t){1}) and it matches ma and t and doesnt match bla I want it to match bla and doesnt match ma and t by adding something to this regex, i know i can write bla, my real-life regex is more complex.

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  • Regex to leave desired string remaining and others removed

    - by m7d
    In Ruby, what regex will strip out all but a desired string if present in the containing string? I know about /[^abc]/ for characters, but what about strings? Say I have the string "group=4&type_ids[]=2&type_ids[]=7&saved=1" and want to retain the pattern group=\d, if it is present in the string using only a regex? Currently, I am splitting on & and then doing a select with matching condition =~ /group=\d/ on the resulting enumerable collection. It works fine, but I'd like to know the regex to do this more directly.

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  • Complex(?) regex: Is expression, but not another

    - by Kieron
    (If you can make a better title, please do) Hi, I need to make sure a string matches the following regex: ^[0-9a-zA-Z]{1}[0-9a-zA-Z\.\-_]*$ (Starts with a letter or number, then any number of letters, numbers, dots, dashes or underscores) But given that, I need to make sure it doesn't match a Guid, my Guid matching reg-ex looks like this (obviously, this needs to be negated in the merged result): ^([0-9a-fA-F]){8}-([0-9a-fA-F]){4}-([0-9a-fA-F]){4}-([0-9a-fA-F]){4}-([0-9a-fA-F]){12}$ The last requirement here is that they must (if it's possible) be merged into a single expression.

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  • A pattern matching an expression that doesn't end with specific sequence

    - by patryk
    I need a regex pattern which matches such strings that DO NOT end with such a sequence: \.[A-z0-9]{2,} by which I mean the examined string must not have at its end a sequence of a dot and then two or more alphanumeric characters. For example, a string /home/patryk/www and also /home/patryk/www/ should match desired pattern and /home/patryk/images/DSC002.jpg should not. I suppose this has something to do with lookarounds (look aheads) but still I have no idea how to make it. Any help appreciated.

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  • What does !! (double exclamation point) mean?

    - by molecules
    In the code below, from a blog post by Alias, I noticed the use of the double exclamation point !!. I was wondering what it meant and where I could go in the future to find explanations for Perl syntax like this. (Yes, I already searched for '!!' at perlsyn). package Foo; use vars qw{$DEBUG}; BEGIN { $DEBUG = 0 unless defined $DEBUG; } use constant DEBUG => !! $DEBUG; sub foo { debug('In sub foo') if DEBUG; ... } UPDATE Thanks for all of your answers. Here is something else I just found that is related The List Squash Operator x!!

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  • UNIX-style RegExp Replace running extremely slowly under windows. Help? EDIT: Negative lookahead ass

    - by John Sullivan
    I'm trying to run a unix regEXP on every log file in a 1.12 GB directory, then replace the matched pattern with ''. Test run on a 4 meg file is took about 10 minutes, but worked. Obviously something is murdering performance by several orders of magnitude. Find: ^(?!.*155[0-2][0-9]{4}\s.*).*$ -- NOTE: match any line NOT starting 155[0-2]NNNN where in is a number 0-9. Replace with: ''. Is there some justifiable reason for my regExp to take this long to replace matching text, or is the program I am using (this is windows / a program called "grepWin") most likely poorly optimized? Thanks. UPDATE: I am noticing that searching for ^(155[0-2]).$ takes ~7 seconds in a 5.6 MB file with 77 matches. Adding the Negative Lookahead Assertion, ?=, so that the regExp becomes ^(?!155[0-2]).$ is causing it to take at least 5-10 minutes; granted, there will be thousands and thousands of matches. Should the negative lookahead assertion be extremely detrimental to performance, and/or a large quantity of matches?

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  • UNIX-style RegExp Replace running extremely slowly under windows. Help?

    - by John Sullivan
    I'm trying to run a unix regEXP on every log file in a 1.12 GB directory, then replace the matched pattern with ''. Test run on a 4 meg file is took about 10 minutes, but worked. Obviously something is murdering performance by several orders of magnitude. Find: ^(?!.*155[0-2][0-9]{4}\s.*).*$ -- NOTE: match any line NOT starting 152[0-2]NNNN where in is a number 0-9. Replace with: ''. Is there some justifiable reason for my regExp to take this long to replace matching text, or is the program I am using (this is windows / a program called "grepWin") most likely poorly optimized? Thanks.

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  • Regular expression for a string containing one word but not another

    - by Chris Stahl
    I'm setting up some goals in Google Analytics and could use a little regex help. Lets say I have 4 URLs http://www.anydotcom.com/test/search.cfm?metric=blah&selector=size&value=1 http://www.anydotcom.com/test/search.cfm?metric=blah2&selector=style&value=1 http://www.anydotcom.com/test/search.cfm?metric=blah3&selector=size&value=1 http://www.anydotcom.com/test/details.cfm?metric=blah&selector=size&value=1 I want to create an expression that will identify any URL that contains the string selector=size but does NOT contain details.cfm I know that to find a string that does NOT contain another string I can use this expression: (^((?!details.cfm).)*$) But, I'm not sure how to add in the selector=size portion. Any help would be greatly appreciated!

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  • Regular expression, how to find all tags A which do not contain tag IMG inside it?

    - by Kirzilla
    Hello, Let's suppose that we have such HTML code. We need to get all <a href=""></a> tags which DO NOT contain img tag inside it. <a href="http://domain1.com"><span>Here is link</span></a> <a href="http://domain2.com" title="">Hello</a> <a href="http://domain3.com" title=""><img src="" /></a> <a href="http://domain4" title=""> I'm the image <img src="" /> yeah</a> I'm using this regular expression to find out all links preg_match_all("!<a[^>]+href=\"?'?([^ \"'>]+)\"?'?[^>]*>(.*?)</a>!is", $content, $out); I can modify it preg_match_all("!<a[^>]+href=\"?'?([^ \"'>]+)\"?'?[^>]*>([^<>]+?)</a>!is", $content, $out); But how can I tell to exclude results containing <img substring inside of <a href=""></a>? Thank you

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  • what is regular expression not generated over {a,b}?

    - by Loop
    Hello all, I am really stuck with these 2 question for over 2 days now. trying to figure out what the question means.... my tutor is out of town too.... write a regular expression for the only strings that are not generated over {a,b} by the expression: (a+b)*a(a+b)*. explain your reasoning. and i tried the second question, do you think is there any better answer than this one? what is regular expression of set of string that contain an odd number of a's or exactly two b's................(a((a|b)(a|b))*|bb).... coz i know to represent any odd length of a's, the RE is a((a|b)(a|b))*

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  • Do you use logical negation operator (!) in "if" statement or check on "== false"

    - by Taras Terebkov
    Hello everyone, I just want to conduct a little survey about code style developers prefer. For me there are two ways to write "if" in such languages as Java, C#, C++, etc. (1) Logical negation operator public void foo() { if (!SessionManager.getInstance().hasActiveSession()) { . . . . . } } (2) Check on "false" public void foo() { if (SessionManager.getInstance().hasActiveSession() == false) { . . . . . } } I always believe that first way is much worst then the second one. Cause usually you don't "read" the code, but "recognize" it in one brief look. And exclamation symbol slipped from your mind, just disturbing you somewhere on the bottom of your unconscious. And only during reading the "if" block below you understand, that the logic is opposite - no sessions in "if" On the other hand in the second way of writing, an eye immediately catches words "SessionManager", "hasActiveSession" and "false". Also for me, the situation with "true" is different. In code like class SessionManager { private bool hasSession; public void foo() { if (hasSession == true) { . . . . . } else { . . . . . } } } I find "true" superfluous. why we repeating the sentence two times? The following is shorter and quicker to catch. class SessionManager { private bool hasSession; public void foo() { if (hasSession) { . . . . . } else { . . . . . } } } What do YOU think, guys?

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  • Boolean Not operator in VBScript

    - by Lumi
    Consider the following two conditionals (involving bitwise comparisons) in VBScript: If 1 And 3 Then WScript.Echo "yes" Else WScript.Echo "no" If Not(1 And 3) Then WScript.Echo "yes" Else WScript.Echo "no" Prints first yes, then no, right? cscript not.vbs Wrong! It prints yes twice! Wait a second, the Not operator is supposed to perform logical negation on an expression. The logical negation of true is false, as far as I know. Must I conclude that it doesn't live up to that promise? How and why and what is going on here? What is the rationale, if any?

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  • Why don't languages include implication as a logical operator?

    - by Maciej Piechotka
    It might be a strange question, but why there is no implication as a logical operator in many languages (Java, C, C++, Python Haskell - although as last one have user defined operators its trivial to add it)? I find logical implication much clearer to write (particularly in asserts or assert-like expressions) then negation with or: encrypt(buf, key, mode, iv = null) { assert (mode != ECB --> iv != null); assert (mode == ECB || iv != null); assert (implies(mode != ECB, iv != null)); // User-defined function }

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