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• named_scope and substings

  - by Philb28

  I have a named_scope in rails that finds episodes by there directors given name named_scope :director_given, lambda { |dr| {:joins => :director, :conditions => ['given = ?', dr]} } It works great but I would like it to also work on substrings one the name. e.g. instead of having to search for 'Lucy' you could just search 'Lu'. P.S. I also have another named scope which does exactly the same thing but on the directors last name. It there a way to combine the two? Thanks,

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• Expression Tree : C#

  - by nettguy

  My understanding of expression tree is : Expression trees are in-memory representation of expression like arithmetic or boolean expression.The expressions are stored into the parsed tree.so we can easily transalate into any other language. Linq to SQL uses expression tree.Normally when our LINQ to SQL query compiler translates it to parsed expression trees.These are passed to Sql Server as T-SQL Statements.The Sql server executes the T-SQL query and sends down the result back.That is why when you execute LINQ to SQL you gets IQueryable<T> not IEnumetrable<T>.Because IQuerybale contains public IQueryable:IEnumerable { Type Element {get;} Expression Expression {get;} IQueryaleProvider Provider {get;} } Questions : Microsoft uses Expression trees to play with LINQ-to-Sql.What are the different ways can i use expression trees to boost my code. Apart from LINQ to SQL,Linq to amazon ,who used expression trees in their applications? Linq to Object return IEnumerable,Linq to SQL return IQueryable ,What does LINQ to XML return?

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• Regex pattern for searches with include and exclude

  - by alex-kravchenko-zmeyp

  I am working on a Regex pattern for searches that should allow optional '+' sign to include in the search and '-' sign to exclude from the search. For example: +apple orange -peach should search for apples and oranges and not for peaches. Also the pattern should allow for phrases in double quotes mixed with single words, for example: "red apple" -"black grape" +orange - you get the idea, same as most of the internet searches. So I am running 2 regular expressions, first to pick all the negatives, which is simple because '-' is required: (?<=[\-]"?)((?<=")(?<exclude>[^"]+)|(?<exclude>[^\s,\+\-"]+)) And second to pick positives, and it is a little more complex because '+' is optional: ((?<=[\+\s]")(?<include>[^\s"\+\-][^"]+))|(?<include>(?<![\-\w]"?)([\w][^,\s\-\+]+))(?<!") Positive search is where I am having a problem, it works fine when I run it in RegexBuddy but when I try in .Net the pattern picks up second word from negative criteria, for example in -"black grape" it picks up word 'grape' even though it ends with double quote. Any suggestions?

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• Python/PyParsing: Difficulty with setResultsName

  - by Rosarch

  I think I'm making a mistake in how I call setResultsName(): from pyparsing import * DEPT_CODE = Regex(r'[A-Z]{2,}').setResultsName("Dept Code") COURSE_NUMBER = Regex(r'[0-9]{4}').setResultsName("Course Number") COURSE_NUMBER.setParseAction(lambda s, l, toks : int(toks[0])) course = DEPT_CODE + COURSE_NUMBER course.setResultsName("course") statement = course From IDLE: >>> myparser import * >>> statement.parseString("CS 2110") (['CS', 2110], {'Dept Code': [('CS', 0)], 'Course Number': [(2110, 1)]}) The output I hope for: >>> myparser import * >>> statement.parseString("CS 2110") (['CS', 2110], {'Course': ['CS', 2110], 'Dept Code': [('CS', 0)], 'Course Number': [(2110, 1)]}) Does setResultsName() only work for terminals?

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• How to handle an "infinite" IEnumerable?

  - by Danvil

  A trivial example of an "infinite" IEnumerable would be IEnumerable<int> Numbers() { int i=0; while(true) { yield return i++; } } I know, that foreach(int i in Numbers().Take(10)) { Console.WriteLine(i); } and var q = Numbers(); foreach(int i in q.Take(10)) { Console.WriteLine(i); } both work fine (and print out the number 0-9). But are there any pitfalls when copying or handling expressions like q? Can I rely on the fact, that they are always evaluated "lazy"? Is there any danger to produce an infinite loop?

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• Regular expression to match one of two video ID's in a Google Video URL

  - by Baldur

  I need to grab the video ID from a Google Video URL. There are two different types of URLs that I need to be able to match: http://video.google.com/videoplay?docid=-3498228245415745977# where I need to be able to match -3498228245415745977 (note the dash; -), and video.google.com/videoplay?docid=-3498228245415745977#docid=2728972720932273543 where I need to match 2728972720932273543. Is there any good regular expression that can match this? This is what I've got so far: @"docid=(-?\d{19}+)" since the video ID seems to be 19 characters except when it's prefixed with the dash. I'm using C# (of which I have very little experience) if that changes anything. P.s. I would also appreciate you review my regular expressions for YouTube (@"[\?&]v=([^&#])";), RedTube (@"/(\d{1,6})") and Vimeo (@"/(\d*)"). I do not expect users to enter the full URL and thus do not match the ^http://\\.?sitename+\\.\\w{2,3}.

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• Numbering Regex Submatches

  - by gentlylisped

  Is there a canonical ordering of submatch expressions in a regular expression? For example: What is the order of the submatches in "(([0-9]{3}).([0-9]{3}).([0-9]{3}).([0-9]{3}))\s+([A-Z]+)" ? a. (([0-9]{3})\.([0-9]{3})\.([0-9]{3})\.([0-9]{3}))\s+([A-Z]+) (([0-9]{3})\.([0-9]{3})\.([0-9]{3})\.([0-9]{3})) ([A-Z]+) ([0-9]{3}) ([0-9]{3}) ([0-9]{3}) ([0-9]{3}) b. (([0-9]{3})\.([0-9]{3})\.([0-9]{3})\.([0-9]{3}))\s+([A-Z]+) (([0-9]{3})\.([0-9]{3})\.([0-9]{3})\.([0-9]{3})) ([0-9]{3}) ([0-9]{3}) ([0-9]{3}) ([0-9]{3}) ([A-Z]+) or c. somthin' else.

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• How to extract URL parameters from a URL with Ruby or Rails?

  - by Flackou

  Hi, I have some URLs, like http://www.example.com/something?param1=value1&param2=value2&param3=value3, and I would like to extract the parameters from these URLs and get them in a Hash. Obviously, I could use regular expressions, but I was just wondering if there was easier ways to do that with Ruby or Rails. I haven't found anything in the Ruby Module 'URI' but perhaps I missed something. In fact, I need a method that would do that : extract_parameters_from_url("http://www.example.com/something?param1=value1&param2=value2&param3=value3") => {:param1 => 'value1', :param2 => 'value2', :param3 => 'value3'} Would you have some advices? Thanks in advance. Julien

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• Python regular expression help

  - by dlw

  Hi SO, I can't seem to create the correct regular expression to extract the correct tokens from my string. Padding the beginning of the string with a space generates the correct output, but seems less than optimal: >>> import re >>> s = '-edge_0triggered a-b | -level_Sensitive c-d | a-b-c' >>> re.findall(r'\W(-[\w_]+)',' '+s) ['-edge_0triggered', '-level_Sensitive'] # correct output Here are some of the regular expressions I've tried, does anyone have a regex suggestion that doesn't involve changing the original string and generates the correct output >>> re.findall(r'(-[\w_]+)',s) ['-edge_0triggered', '-b', '-level_Sensitive', '-d', '-b', '-c'] >>> re.findall(r'\W(-[\w_]+)',s) ['-level_Sensitive'] Thanks -- DW

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• Math with interpolated variables?

  - by Idan Gazit

  Consider the following sass: $font-size: 18; $em: $font-size; $column: $font-size * 3; // The column-width of my grid in pixels $gutter: $font-size * 1; // The gutter-width of my grid in pixels $gutter-em: #{$gutter / $em}em; // The gutter-width in ems. $column-em: #{$column / $em}em; // The column-width in ems; $foo = $gutter-em / 2; // This results in a value like "1em/2". :( $bar = ($gutter-em / 2); // this doesn't work either, same as above. How can I generate a $foo that works, and that I can reuse further in other expressions?

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• How can I replace only the last occurence of an number in a string with php?

  - by Shawn

  How would you change this: a-10-b-19-c into something like this: a-10-b-20-c using regular expressions in PHP? The only solution I've found so far is: reverse the original string - "c-91-b-01-a" find the first number - "91" reverse it - "19" turn in into a number (parseInt) - 19 add 1 to it (+1) - 20 turn it into a string again (toString) - "20" reverse it again - "02" replace the original match with this new number - "c-02-b-01-a" reverse the string - "a-10-b-20-c" I was hoping someone on SO would have a simpler way to do this... Anyone?

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• Why does Excel expose an 'Evaluate' method at all?

  - by jtolle

  A few questions have come up recently involving the Application.Evaluate method callable from Excel VBA. The old XLM macro language also exposes an EVALUATE() function. Both can be quite useful. Does anyone know why the general expression evaluator is exposed, though? My own hunch is that Excel needed to give people a way to get ranges from string addresses, and to get the value of named formulas, and just opening a portal to the expression evaluator was the easiest way. But of course you don't need the ability to evaluate arbitrary expressions just to do that. Application.Evaluate seems kind of...unfinished. It isn't very well documented, and there are quite a few quirks and limitations (as described by Charles Williams here: http://www.decisionmodels.com/calcsecretsh.htm) with what is exposed. I suppose the answer could be simply "why not expose it?", but I'd be interested to know what design decisions led to this feature. Failing that, I'd be interested to hear other hunches.

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• Efficient data structure design

  - by Sway

  Hi there, I need to match a series of user inputed words against a large dictionary of words (to ensure the entered value exists). So if the user entered: "orange" it should match an entry "orange' in the dictionary. Now the catch is that the user can also enter a wildcard or series of wildcard characters like say "or__ge" which would also match "orange" The key requirements are: * this should be as fast as possible. * use the smallest amount of memory to achieve it. If the size of the word list was small I could use a string containing all the words and use regular expressions. however given that the word list could contain potentially hundreds of thousands of enteries I'm assuming this wouldn't work. So is some sort of 'tree' be the way to go for this...? Any thoughts or suggestions on this would be totally appreciated! Thanks in advance, Matt

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• Merging MySQL row entries into a single row

  - by Derrick

  I've got two tables, one for listings and another representing a list of tags for the listings table. In the listings table the tag ids are stored in a field called tags as 1-2-3-. This has worked out very well for me (regular expressions and joins to separate and display the data), but I now need to pull the titles of those tags into a single row. See below. listings table id tags 1 1-2-3- 2 4-5-6- tags table id title 1 pig 2 dog 3 cat 4 mouse 5 elephant 6 duck And what I need to produce out of the listings table is: id tags 2 mouse, elephant, duck

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• declarative authorization and has_and_belongs_to_many

  - by Michael Balsiger

  Hi, I have a little problem with declarative-authorization. I have a User and Role Model with a has_and_belongs_to_many association. I've created a Role named :moderator in my authorization_rules.rb Is it possible that a User with the Role Moderator only gets the Users that have the Moderator Role assigned to it?? -- User.with_permissions_to(:index) I thought it would be possible like that: role :moderator do has_permission_on :users, :to => :index do if_attribute :roles => contains { ????? } end end I also created a named_scope in my User Model because I thought it would help... class User has_and_belongs_to_many :roles named_scope :by_role, lambda { |role| { :include => :roles, :conditions => {"roles.name" => role} } } end Does anyone knows if it's possible to do this with declarative_authorization? Thanks for your help!

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• Regular Expression for finding phone numbers

  - by Rocky

  Hello Everyone, I am new to Stackoverflow and I have a quick question. Let's assume we are given a large number of HTML files (large as in theoretically infinite). How can I use Regular Expressions to extract the list of Phone Numbers from all those files? Explanation/expression will be really appreciated. The Phone numbers can be any of the following formats: (123) 456 7899 (123).456.7899 (123)-456-7899 123-456-7899 123 456 7899 1234567899 Thanks a lot for all your help and have a good one!

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• Using C# and gppg, how would I construct an abstract syntax tree?

  - by Rupert

  Is there a way to do this almost out-of-the-box? I could go and write a big method that would use the collected tokens to figure out which leaves should be put in which branches and in the end populate a TreeNode object, but since gppg already handled everything by using supplied regular expressions, I was wondering if there's an easier way? Even if not, any pointers as to how best to approach the problem of creating an AST would be appreciated. Apologies if I said anything silly, I'm only just beginning to play the compiler game. :)

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• Do I need to include the 'this' when using a property name in a closure?

  - by Scott Whitlock

  I'm using a list of Actions to store an undo history for an object. Let's say I have a property of my object called myChildObject and it's being changed, so I want to store the undo action where I would set it back to it's current value: public class Class1 { public Class1() { } private readonly List<Action> m_undoActions = new List<Action>(); private SomeObject myChildObject { get; set; } public void ChangeState(SomeObject newChildObject) { // copies the reference SomeObject existingObject = myChildObject; m_undoActions.Add(() => myChildObject = existingObject); myChildObject = newChildObject; } } Looking at the lambda expression, existingObject is a local variable, so it's using a closure to pass a reference to that variable, but what about the property myChildObject? Do I need to use 'this' to preface it? Do I need to make a copy of the 'this' reference to a local variable first? Thanks for helping me understand this closure stuff.

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• How can I remove sensitive data from the debug_backtrace function?

  - by RenderIn

  I am using print_r(debug_backtrace(), true) to retrieve a string representation of the debug backtrace. This works fine, as print_r handles recursion. When I tried to recursively iterate through the debug_backtrace() return array before turning it into a string it ran into recursion and never ended. Is there some simple way I can remove certain sensitive key/value pairs from the backtrace array? Perhaps some way to turn the array to a string using print_r, then back to an array with the recursive locations changed to the string RECURSION, which I could the iterate through. I don't want to execute regular expressions on the string representation if possible.

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• A compiler for automata theory

  - by saadtaame

  I'm designing a programming language for automata theory. My goal is to allow programmers to use machines (DFA, NFA, etc...) as units in expressions. I'm confused whether the language should be compiled, interpreted, or jit-compiled! My intuition is that compilation is a good choice, for some operations might take too much time (converting NFA's to equivalent DFA's can be expensive). Translating to x86 seems good. There is one issue however: I want the user to be able to plot machines. Any ideas?

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• Do comments slow down an interpreted language?

  - by mvid

  I am asking this because I use Python, but it could apply to other interpreted languages as well (ruby, php). Whenever I leave a comment in my code, is it slowing down the interpreter? My limited understanding of an interpreter is that it reads program expressions in as strings and converts those strings into code. It seems that every time it parses a comment, that is wasted time. Is this the case? Is there some convention for comments in interpreted languages, or is the effect negligible?

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• Can a Domain Specific Language (DSL) be localized?

  - by michielvoo

  I have never written a DSL, but I am considering it as a feature for a new project (hypothetical). It would be for end users to be able to express in natural language concepts such as weekdays between 10 and 11 except on the first monday of the month. Dutch users might write weekdagen tussen 10 en 11 behalve op de eerste maandag van de maand. In this case the position of the words seems to match, but there may be expressions where the position of verbs/nouns etc. could be different between languages. I realise the obvious answer (it depends). I am a .NET developer and I consider using Boo but I'm open to suggestions. I need to understand wether each translation requires rewriting a part of the implementation (which part) or if there is a way to do actual translations, maybe in some sort of preprocessor. Thanks!

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• What is the purpose of Java's unary plus operator?

  - by Syntactic

  Java's unary plus operator appears to have come over from C, via C++. As near as I can tell, it has the following effects: promotes its operand to int, if it's not already an int or wider unboxes its operand, if it's a wrapper object complicates slightly the parsing of evil expressions containing large numbers of consecutive plus signs It seems to me that there are better (or, at least, clearer) ways to do all of these things. In this SO question, concerning the counterpart operator in C#, someone said that "It's there to be overloaded if you feel the need." But in Java, one cannot overload any operator. So does this operator exist in Java just because it existed in C++?

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• Are Scala "continuations" just a funky syntax for defining and using Callback Functions?

  - by Alex R

  And I mean that in the same sense that a C/Java for is just a funky syntax for a while loop. I still remember when first learning about the for loop in C, the mental effort that had to go into understanding the execution sequence of the three control expressions relative to the loop statement. Seems to me the same sort of effort has to be applied to understand Continuations (in Scala and I guess probably other languages). And then there's the obvious follow-up question... if so, then what's the point? It seems like a lot of pain (language complexity, programmer errors, unreadable programs, etc) for no gain.

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• Adding two Set[Any]

  - by Alex Boisvert

  Adding two Set[Int] works: Welcome to Scala version 2.8.1.final (Java HotSpot(TM) Server VM, Java 1.6.0_23). Type in expressions to have them evaluated. Type :help for more information. scala> Set(1,2,3) ++ Set(4,5,6) res0: scala.collection.immutable.Set[Int] = Set(4, 5, 6, 1, 2, 3) But adding two Set[Any] doesn't: scala> Set[Any](1,2,3) ++ Set[Any](4,5,6) <console>:6: error: ambiguous reference to overloaded definition, both method ++ in trait Addable of type (xs: scala.collection.TraversableOnce[Any])scala.collection.immutable.Set[Any] and method ++ in trait TraversableLike of type [B >: Any,That](that: scala.collection.TraversableOnce[B])(implicit bf: scala.collection.generic.CanBuildFrom[scala.collection.immutable.Set[Any],B,That])That match argument types (scala.collection.immutable.Set[Any]) Set[Any](1,2,3) ++ Set[Any](4,5,6) ^ Any suggestion to work around this error?

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