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  • Fast exchange of data between unmanaged code and managed code

    - by vizcaynot
    Hello: Without using p/invoke, from a C++/CLI I have succeeded in integrating various methods of a DLL library from a third party built in C. One of these methods retrieves information from a database and stores it in different structures. The C++/CLI program I wrote reads those structures and stores them in a List<, which is then returned to the corresponding reading and use of an application programmed completely in C#. I understand that the double handling of data (first, filling in several structures and then, filling all of these structures into a list<) may generate an unnecessary overload, at which point I wish C++/CLI had the keyword "yield". Depending on the above scenario, do you have recommendations to avoid or reduce this overload? Thanks.

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  • Is there any significant benefit to reading string directly from control instead of moving it into a

    - by Kevin
    sqlInsertFrame.Parameters.AddWithValue("@UserName", txtUserName.txt); Given the code above...if I don't have any need to move the textbox data into a string variable, is it best to read the data directly from the control? In terms of performance, it would seem smartest to not create any unnecessary variables which use up memory if its not needed. Or is this a situation where its technically true but doesn't yield any real world results due to the size of the data in question. Forgive me, I know this is a very basic question.

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  • Anonymous iterators blocks in Clojure?

    - by Checkers
    I am using clojure.contrib.sql to fetch some records from an SQLite database. (defn read-all-foo [] (let [sql "select * from foo"] (with-connection *db* (with-query-results res [sql] (into [] res))))) Now, I don't really want to realize the whole sequence before returning from the function (i.e. I want to keep it lazy), but if I return res directly or wrap it some kind of lazy wrapper (for example I want to make a certain map transformation on result sequence), SQL bindings will be gone after I return, so realizing the sequence will throw an error. How can I enclose the whole function in a closure and return a kind of anonymous iterator block (like yield in C# or Python)? Or is there another way to return a lazy sequence from this function?

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  • How can I collapse a dataframe by some variables, taking mean across others

    - by Alex Holcombe
    I need to summarize a data frame by some variables, ignoring the others. This is sometimes referred to as collapsing. E.g. if I have a dataframe like this: Widget Type Energy egg 1 20 egg 2 30 jap 3 50 jap 1 60 Then collapsing by Widget, with Energy the dependent variable, Energy~Widget, would yield Widget Energy egg 25 jap 55 In Excel the closest functionality might be "Pivot tables" and I've worked out how to do it in python (http://alexholcombe.wordpress.com/2009/01/26/summarizing-data-by-combinations-of-variables-with-python/), and here's an example with R using doBy library to do something very related (http://www.mail-archive.com/[email protected]/msg02643.html), but is there an easy way to do the above? And even better is there anything built into the ggplot2 library to create plots that collapse across some variables?

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  • Divide numpy array

    - by BandGap
    Hi all I have some data represented in a 1300x1341 matrix. I would like to split this matrix in several pieces (e.g. 9) so that I can loop over and process them. The data needs to stay ordered in the sense that x[0,1] stays below (or above if you like) x[0,0] and besides x[1,1]. Just like if you had imaged the data, you could draw 2 vertical and 2 horizontal lines over the image to illustrate the 9 parts. If I use numpys reshape (eg. matrix.reshape(9,260,745) or any other combination of 9,260,745) it doesn't yield the required structure since the above mentioned ordering is lost... Did I misunderstand the reshape method or can it be done this way? What other pythonic/numpy way is there to do this?

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  • heirarchial data from self referencing table in tree form

    - by Beta033
    Ii looks like this has been asked and answered in all the simple cases, excluding the one that i'm having trouble with. I've tried using a recursive CTE to generate this, however maybe a cursor would be better? or maybe a set of recursive functions will do the trick? Can this be done in a cte? consider the following table PrimaryKey ParentKey 1 NULL 2 1 3 6 4 7 5 2 6 1 7 NULL should yield PK 1 -2 --5 -6 --3 7 -4 where the number of - marks equal the depth, my primary difficulty is the ordering.

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  • How to partition a plane

    - by puls200
    Let's say I have a fixed number (X) of points, e.g. coordinates within a given plane (I think you can call it a 2-D point cloud). These points should be partitioned into Y polygons where Y < X. The polygons should not overlap. It would be wonderful if the polygons were konvex (like a Voronoi diagram). Imagine it like locations forming countries. For example, I have 12 points and want to create 3 polygons with 4 points each. I thought about creating a grid which covers the points. Then iterate across the points, assigning them to the closest grid cells. Maybe I miss the obvious? I am sure there are better solutions. Thanks, Daniel I just found an optimization (kmeans++) .Maybe this will yield better results..

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  • Testing methods called on yielded object

    - by Todd R
    I have the following controller test case: def test_showplain Cleaner.expect(:parse).with(@somecontent) Cleaner.any_instance.stubs(:plainversion).returns(@returnvalue) post :showplain, {:content => @somecontent} end This works fine, except that I want the "stubs(:plainversion)" to be an "expects(:plainversion)". Here's the controller code: def showplain Cleaner.parse(params[:content]) do | cleaner | @output = cleaner.plainversion end end And the Cleaner is simply: class Cleaner ### other code and methods ### def self.parse(@content) cleaner = Cleaner.new(@content) yield cleaner cleaner.close end def plainversion ### operate on @content and return ### end end Again, I can't figure out how to reliably test the "cleaner" that is made available from the "parse" method. Any suggestions?

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  • C# - implementing GetEnumerator() for a collection inherited from List<string>

    - by Vojtech
    Hi, I am trying to implement FilePathCollection. Its items would be simple file names (without a path - such as "image.jpg"). Once the collection is used via foreach cycle, it should return the full path created by concatenating with "baseDirectory". How can I do that? public class FilePathCollection : List<string> { string baseDirectory; public FileCollection(string baseDirectory) { this.baseDirectory = baseDirectory; } new public System.Collections.IEnumerator GetEnumerator() { foreach (string value in this._list) //this does not work because _list is private yield return baseDirectory + value; } } Thanks in advance! :-)

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  • How do you encode an apostrophe so that it's searchable in mysql?

    - by Yegor
    I don't think that was the most clear question, but an example should make it a little clearer. I have a table filled with movie names, some of which contain apostrophes. I have a search box which is used to find movies. If I perform searches via mov_title = '$search_keywords' it all works, but this method will not yield any results for partial searches, so I have to use this mov_title LIKE '%$search_keywords%' This method works fine for titles that are A-Za-z0-9, but if a title has an apostrophe, it's not able to find the movie, even if I do an exact match. Before the titles are stored in the DB, I put them through this: $search_keywords = htmlspecialchars(mysql_escape_string($_GET["search_keywords"])); So in the DB, there is a forward slash before every single apostrophe. The only way to match a movie title with an apostrophe is to physically put a forward slash in front of the apostrophe, in the search box. This seems so trivial, and I'm sure the solution is painfully obvious, but I'm just not seeing it.

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  • Get a value from hashtable by a part of its key

    - by htf
    Hi. Say I have a Hashtable<String, Object> with such keys and values: apple => 1 orange => 2 mossberg => 3 I can use the standard get method to get 1 by "apple", but what I want is getting the same value (or a list of values) by a part of the key, for example "ppl". Of course it may yield several results, in this case I want to be able to process each key-value pair. So basically similar to the LIKE '%ppl%' SQL statement, but I don't want to use a (in-memory) database just because I don't want to add unnecessary complexity. What would you recommend?

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  • What is the best way to set default values in ActiveRecord?

    - by ryw
    What is the best way to set default value in ActiveRecord? I see a post from Pratik that describes an ugly, complicated chunk of code: http://m.onkey.org/2007/7/24/how-to-set-default-values-in-your-model class Item < ActiveRecord::Base def initialize_with_defaults(attrs = nil, &block) initialize_without_defaults(attrs) do setter = lambda { |key, value| self.send("#{key.to_s}=", value) unless !attrs.nil? && attrs.keys.map(&:to_s).include?(key.to_s) } setter.call('scheduler_type', 'hotseat') yield self if block_given? end end alias_method_chain :initialize, :defaults end YUCK! I have seen the following examples googling around: def initialize super self.status = ACTIVE unless self.status end and def after_initialize return unless new_record? self.status = ACTIVE end I've also seen people put it in their migration, but I'd rather see it defined in the model code. What's the best way to set default value for fields in ActiveRecord model?

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  • matlab: putting a circled number onto a graph

    - by Jason S
    I want to put a circled number on a graph as a marker near (but not on) a point. Sounds easy, but I also want to be invariant of zoom/aspect ratio changes. Because of this invariant, I can't draw a circle as a line object (without redrawing it upon rescale); if I use a circle marker, I'd have to adjust its offset upon rescale. The simplest approach I can think of is to use the Unicode or Wingdings characters ① ② ③ etc. in a string for the text() function. But unicode doesn't seem to work right, and the following sample only works with ① and not for the other numbers (which yield rectangle boxes): works: clf; text(0.5,0.5,char(129),'FontName','WingDings') doesn't work (should be a circled 2): clf; text(0.5,0.5,char(130),'FontName','WingDings') What gives, and can anyone suggest a workaround?

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  • How to update a table in database using LINQ in F#?

    - by sudaly
    I have seen plenty of examples on how to query the database but nothing on how to update records. Below is the simple code that I wrote to retrieve a table, but can someone explain me how can I modify a field, say lastActiveDate, and update the table on the database Thank you, suday open System open Microsoft.FSharp.Linq let connString = "Server=localhost;Database=myDb;Trusted_Connection=True;" let db = new MyDb(connString) db.Log <- System.Console.Out let res = Query.query <@ seq { for users in db.userAccounts do yield users } @> |> List.ofSeq printfn "Totla users: %d" res.Length

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  • How to create string "Version 1.0" in C#

    - by Rohit
    I have to store versionName of a template. VersionName is autoincremented.If last versionName is "Version 1.0", next should be "version 2.0". First time when a template is created, I have to store "Version 1.0". I am using VersionName = "Version "+((LatestVersion+1).ToString()) LatestVersion holds the last version which is 0 in case added for first time. This seems to be a ugly workaround and doesnot even yield Version 1.0. it yields Version 1. I Tried with Version class as well,it does not work. How to accomplish this.Please suggest

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  • C++ Types Impossible to Name

    - by Kirakun
    While reading Wikipedia's page on decltype, I was curious about the statement, Its [decltype's] primary intended use is in generic programming, where it is often difficult, or even impossible, to name types that depend on template parameters. While I can understand the difficulty part of that statement, what is an example where there is a need to name a type that cannot be named under C++03? EDIT: My point is that since everything in C++ has a declaration of types. Why would there ever be a case where it is impossible to name a type? Furthermore, aren't trait classes designed to yield type informations? Could trait classes be an alternative to decltype?

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  • Validating primitive types in ASP.NET MVC

    - by Alex
    I've implemented the following classes to validate data public abstract class Validated { public bool IsValid { get { return (GetRuleViolations().Count() == 0); } } public abstract IEnumerable<RuleViolation> GetRuleViolations(); } public partial class User: Validated { public override IEnumerable<RuleViolation> GetRuleViolations() { if (this.Age < 1) yield return new RuleViolation("Age can't be less than 1"); } } It works great! When the form is submitted I just do if (user.IsValid == false) blah... But I still need to validate that the Age is an integer int a = 0; if (!int.TryParse(age, out a)) { error = "Not integer"; // ... } How can I move this to my model?

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  • What is the best design to this class?

    - by HPT
    assume this class: public class Logger { static TextWriter fs = null; public Logger(string path) { fs = File.CreateText(path); } public static void Log(Exception ex) { ///do logging } public static void Log(string text) { ///do logging } } and I have to use this like: Logger log = new Logger(path); and then use Logger.Log() to log what I want. the question is: is this a good design? to instantiate a class and then always call it's static method? any suggestion yield in better design is appreciated.

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  • hierarchical data from self referencing table in tree form

    - by Beta033
    It looks like this has been asked and answered in all the simple cases, excluding the one that I'm having trouble with. I've tried using a recursive CTE to generate this; however maybe a cursor would be better? Or maybe a set of recursive functions will do the trick? Can this be done in a cte? consider the following table PrimaryKey ParentKey 1 NULL 2 1 3 6 4 7 5 2 6 1 7 NULL should yield PK 1 -2 --5 -6 --3 7 -4 where the number of - marks equal the depth, my primary difficulty is the ordering.

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  • Anonymous iterator blocks in Clojure?

    - by Checkers
    I am using clojure.contrib.sql to fetch some records from an SQLite database. (defn read-all-foo [] (with-connection *db* (with-query-results res ["select * from foo"] (into [] res)))) Now, I don't really want to realize the whole sequence before returning from the function (i.e. I want to keep it lazy), but if I return res directly or wrap it some kind of lazy wrapper (for example I want to make a certain map transformation on result sequence), SQL-related bindings will be reset and connection will be closed after I return, so realizing the sequence will throw an exception. How can I enclose the whole function in a closure and return a kind of anonymous iterator block (like yield in C# or Python)? Or is there another way to return a lazy sequence from this function?

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  • Any chances to imitate times() Ruby method in C#?

    - by Alexander Prokofyev
    Every time I need to do something N times inside an algorithm using C# I write this code for (int i = 0; i < N; i++) { ... } Studying Ruby I have learned about method times() which can be used with the same semantics like this N.times do ... end Code fragment in C# looks more complex and we should declare useless variable i. I tried to write extension method which returns IEnumerable, but I am not satisfied with the result because again I have to declare a cycle variable i. public static class IntExtender { public static IEnumerable Times(this int times) { for (int i = 0; i < times; i++) yield return true; } } ... foreach (var i in 5.Times()) { ... } Is it possible using some new C# 3.0 language features to make N times cycle more elegant?

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  • Java Authenticator on a per connection basis?

    - by Martijn Laarman
    I'm building an Eclipse plugin that talks to a REST interface which uses Basic Authentication. When the authentication fails I would like to popup my plugin's settings dialog and retry. Normally I could use the static Authenticator.setDefault() to setup an authenticator for all HttpURLConnection's for this, but since I am writing a plugin I don't want to overwrite Eclipse's default Authenticator (org.eclipse.ui.internal.net.auth); I thought of setting my custom Authenticator before loading and putting Eclipse's default back afterwards, but I imagine this will cause all sorts of race issues with multithreading so I quickly lost that notion. Google searches yield all sorts of results basically telling me it's not possible: The Java URLConnection API should have a setAuthenticator(Authenticator) method for making it easier to use this class in multi-threaded context where authentication is required. Source If applications contains few third party plugins and each plugin use its own Authenticator what we should do? Each invocation of "Authenticator.setDefault()" method rewrite previously defined Authenticator... Source Are there any different approaches that might help me overcome this issue?

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  • Algorithm: Removing as few elements as possible from a set in order to enforce no subsets.

    - by phimuemue
    Hello, I got a problem which I do not know how to solve: I have a set of sets A = {A_1, A_2, ..., A_n} and I have a set B. The target now is to remove as few elements as possible from B (creating B'), such that, after removing the elements for all 1 <= i <= n, A_i is not a subset of B'. For example, if we have A_1 = {1,2}, A_2 = {1,3,4}, A_3={2,5}, and B={1,2,3,4,5}, we could e.g. remove 1 and 2 from B (that would yield B'={3,4,5}, which is not a superset of one of the A_i). Does anybody know an algorithm for determining the (minimal number of) elements to be removed?

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  • C++ volatile required when spinning on boost::shared_ptr operator bool()?

    - by JaredC
    I have two threads referencing the same boost::shared_ptr: boost::shared_ptr<Widget> shared; On thread is spinning, waiting for the other thread to reset the boost::shared_ptr: while(shared) boost::thread::yield(); And at some point the other thread will call: shared.reset(); My question is whether or not I need to declare the shared pointer as volatile to prevent the compiler from optimizing the call to shared.operator bool() out of the loop and never detecting the change? I know that if I were simply looping on a variable, waiting for it to reach 0 I would need volatile, but I'm not sure if boost::shared_ptr is implemented in such a way that it is not necessary here.

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  • averaging matrix efficiently

    - by user248237
    in Python, given an n x p matrix, e.g. 4 x 4, how can I return a matrix that's 4 x 2 that simply averages the first two columns and the last two columns for all 4 rows of the matrix? e.g. given: a = array([[1, 2, 3, 4], [5, 6, 7, 8], [9, 10, 11, 12], [13, 14, 15, 16]]) return a matrix that has the average of a[:, 0] and a[:, 1] and the average of a[:, 2] and a[:, 3]. I want this to work for an arbitrary matrix of n x p assuming that the number of columns I am averaging of n is obviously evenly divisible by n. let me clarify: for each row, I want to take the average of the first two columns, then the average of the last two columns. So it would be: 1 + 2 / 2, 3 + 4 / 2 <- row 1 of new matrix 5 + 6 / 2, 7 + 8 / 2 <- row 2 of new matrix, etc. which should yield a 4 by 2 matrix rather than 4 x 4. thanks.

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