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• sum of timespans

  - by frenchie

  I have a collection of objects that include a timespan variable: MyObject { TimeSpan TheDuration {get;set;} } I want to use linq to sum those times. Of course, (from r in MyCollection select r.TheDuration).Sum(); doesn't work! I'm thinking of changing the datatype of TheDuration to an int and then summing it and converting the sum to a TimeSpan. That'll be messy because each TheDuration in my collection is used in as a timespan somewhere else. Any suggestion on this summation?

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• Multiple row insertion in a faster way

  - by Cyborgo

  Hi, I am using rails and I am trying to insert new rows into the table. The data comes from a text file and I created hash with one of the attribute as key. Then I find all the keys that are currently not in the table. Then I need to insert all of them into the table with all the attributes that I saved in hash. newvals.each{ |x| author = Author.create(:first => x, :second => hash[x][0], :third => hash[x][1]) author.save } This has lot of overhead as it makes an SQL update one at time. The newals array is usually quite big around the size of 20-30k. I know create can insert multiple objects at once, but I cant seem to figure out how. Is there any way to get this done. Thanks.

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• How much Java should I have learnt before trying Android programming?

  - by Sidney Yin

  Hi - I have been seeking beginner learning books in Android, and of course found out that I should learn Java first. So I began studying Java and now I am quite comfortable with objects, classes, inheritance, interfaces, and just moved onto Layouts in Swing as well as Swing Features. But I am starting to wonder.... do I know enough about Java now? Can I start programming Android yet? Of course I can keep going in Java, but have been itching to begin programming Android apps. Any definitive answer here about how much Java I need to know before Android? Thanks so much!

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• Solve Physics exercise by brute force approach..

  - by Nils

  Being unable to reproduce a given result. (either because it's wrong or because I was doing something wrong) I was asking myself if it would be easy to just write a small program which takes all the constants and given number and permutes it with a possible operators (* / - + exp(..)) etc) until the result is found. Permutations of n distinct objects with repetition allowed is n^r. At least as long as r is small I think you should be able to do this. I wonder if anybody did something similar here..

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• Excel Interop: Fastest way to change color of portions of text in a huge range of cells

  - by Kyopaxa

  There some articles about the fastest way to write data using Excel interop assigning directly an Array of data to the value of the range. Like: string[,] multidimensionalArrayData = new string[200, 3]; // (...) Fill multidimensionalArrayData with your data dataSheet.Range["A1:C200"].Value = multidimensionalArrayData; There are also some articles about how to change the Font color of a specific portion of text, for example (VB this time): With ActiveCell.Characters(Start:=3, Length:=3).Font .Name = "Arial" .FontStyle = "Regular" .Size = 10 .Color = "Red" .ThemeFont = xlThemeFontNone End With The question now is, what would be the fastest way to change the color of specific portions of text for thousands of cells? Currently, in my C# code, I have to do it cell by cell, with a horrible performance hit. Is there a way to fill an array of 'Characters' objects in C# and pass that array to a range in one go? Any other solutions?

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• Getting the last member of a group on an intermediary M2M

  - by rh0dium

  If we look at the existing docs, what is the best way to get the last member added? This is similar to this but what I want to do is to be able to do this. group = Group.objects.get(id=1) group.get_last_member_added() #This is by ('-date_added') <Person: FOO> I think the best way is through a manager but how do you do this on an intermediary model? class Person(models.Model): name = models.CharField(max_length=128) def __unicode__(self): return self.name class Group(models.Model): name = models.CharField(max_length=128) members = models.ManyToManyField(Person, through='Membership') def __unicode__(self): return self.name class Membership(models.Model): person = models.ForeignKey(Person) group = models.ForeignKey(Group) date_joined = models.DateField() invite_reason = models.CharField(max_length=64)

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• Why delete and recreate a querydef object when you can just change the .SQL property?

  - by dblE

  Do you remember the venerable old Microsoft Query by Form (QBF) VBA example from back in the day link that recommended that you delete an existing query and then recreate it dynamically?: On Error Resume Next db.QueryDefs.Delete ("qryResults") On Error GoTo 0 Set qdf = db.CreateQueryDef("qryResults", "SELECT p.*... Why not just change the SQL property of the querydef object? qdf.SQL = "SELECT p.*... I am wondering if anyone knows why the MS engineers wrote an example that suggests that you delete and then recreate a query instead of simply changing the SQL property? I would guess that the act of deleting and recreating objects over time could contribute to corruption and bloating in your front end, not to mention changing the SQL property is so much simpler. Does anyone have more insight into this?

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• How to calculate deceleration rate of a flipping coin (in c)?

  - by Horace Ho

  A flipping coin on table will slow down and drop to the table surface, facing up or down. How can I calculate the flip-per-second declaration rate over time? For example, assuming the coin is at 10 flipping per second when it starts how long will it take to stop? For each second (9, 8, 7, 6 ... 3, 2, 1, stop), how is the flipping rate changed? Friction can be approximated as some real world objects (say, a metallic coin on a wooden table). Thanks!

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• Good Design for Initialization of Static Array

  - by jplot

  I have a question regarding good design in C++. I have a class A, and all objects of this class use an integer array of constant values (they should share the same array, as their values are constant). The array needs to be computed (just once) before any object A. I thought about having another class B which contains the integer array as a static member, an init() method which would fill this array according to some formula and a static boolean flag initialized (if this variable if true then the init() method would do nothing), but I'm not sure this is the best way to solve my design issue. So my question is, what would be a good design/way to accomplish this ? Thanks in advance.

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• .NET project: unified wrapper for object databases.

  - by Steve

  I am considering doing a project which would provide unified API and tools (import/export, etc.) for object databases (e.g. Caché, Objectivity) for .NET. It would provide: schema generation from CLR classes, generation of C# classes from given OODBMs schema, API for deleting, creating and updating objects, Linq provider, API for calling object's methods on DB server, some of OODBMs provide some kind of SQL support, so API for this, providers for Caché and Objectivity in first phase. Does any project which implements any of above exist? Can this be achieved with NHibernate dialects? or are OODBMs so different than RDBMs that it worth doing separate framework for them?

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• Can I play any Buffer only once at a given time?

  - by mystify

  From the OpenAL documentation: The basic OpenAL objects are a Listener, a Source, and a Buffer. There can be a large number of Buffers, which contain audio data. Each buffer can be attached to one or more Sources My problem is, that I have one sound file which I need to play multiple times per second, at the same time. The sound is 2 seconds long. So it will overlap. Would I need multiple filled buffers for this (= multiple times that sound in memory)? If I would attach one Buffer to multiple Sources, would I be able to play the sound 10 times, overlapping itself, with just one copy in memory? Or would I still have to deal with 10 copies of that sound in memory?

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• Common strategies to deal with rounding errors in currency-intensive soft?

  - by Max

  What is your advice on: compensation of accumulated error in bulk math operations on collections of Money objects. How is this implemented in your production code? (things like variable rounding, etc...) theory behind rounding in accountancy. any literature on topic. I currently read Fowler. He mentions Money type, but says nothing on strategies. Older posts on money-rounding (here, and here) do not provide a details and formality I need. Thanks for help.

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• access a property via string with array in php?

  - by sprugman

  (This is in drupal, but I don't really think that matters.) I have a big list of properties that I need to map between two objects, and in one, the value that I need to map is buried inside an array. I'm hoping to avoid hard-coding the property names in the code. If I have a class like this: class Product { public $colors, $sizes; } I can access the properties like this: $props = array('colors', 'sizes'); foreach ($props as $p) { $this->$p = $other_object->$p; } As far as I can tell, if each of the properties on the left are an array, I can't do this: foreach ($props as $p) { $this->$p[0]['value'] = $other_object->$p; } Is that correct, or am I missing some clever way around this?

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• memory leak in Zend_Db_Table_Row?

  - by Vincenzo

  This is the code I have: <?php $start = memory_get_usage(); $table = new Zend_Db_Table('user'); for ($i = 0; $i < 5; $i++) { $row = $table->createRow(); $row->name = 'Test ' . $i; $row->save(); unset($row); echo (memory_get_usage() - $start) . "\n"; } This is what I see: 90664 93384 96056 98728 101400 Isn't it a memory leak? When I have 500 objects to insert into DB in one script I'm getting memory overflow. Can anyone help?

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• Merging elements in a scala list

  - by scompt.com

  I'm trying to port the following Java snippet to Scala. It takes a list of MyColor objects and merges all of the ones that are within a delta of each other. It seems like a problem that could be solved elegantly using some of Scala's functional bits. Any tips? List<MyColor> mergedColors = ...; MyColor lastColor = null; for(Color aColor : lotsOfColors) { if(lastColor != null) { if(lastColor.diff(aColor) < delta) { lastColor.merge(aColor); continue; } } lastColor = aColor; mergedColors.add(aColor); }

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• Why does `Array(0,1,2) == Array(0,1,2)` not return the expected result?

  - by soc

  As far as I understand, Scala's == defines the natural equality of two objects. I expected that Array(0,1,2) == Array(0,1,2) compares the natural equality e. g. checks if all elements of the array return true when compared with the corresponding elements of the other array. People told me that Scala's Array is just a Java [] which only compares identity. But Scala's String is also just a Java String but Scala overrides equals to compare natural equality. I wonder why Array's equals method was not overridden, too. Thank you for your thoughts!

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• Pointers and collection of pointers in C++. How to properly delete.

  - by Julen

  Hello, This is a newbe question but I have alwasy doubts with pointers in C++. This is the situation. I have a class A which as a collection (a vector actually) of pointers of class B. This same class A has another collection of pointers to class C. Finally the objects of class B have also a collection to pointers to class C which point to the same instances the class A points to. My question is, if I delete a member of class-C-type pointer in class B, what happens to the pointer in class A that points to the deleted instance of class C? How this situation has to be treated? Thanks a lot in advance! Julen.

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• Tied up with injection implemented with setter functions

  - by puudeli

  Hi, I'm trying to use Scala as part of an existing Java application and now I run into an issue with dependencies injected with a setter method (no DI frameworks in this part of code). How is this handled in a Scala way? In Scala both val and var require to be initialized when declared but I can't do that, since the Java setters inject objects that implement a certain interface and interfaces are abstract and can not be instantiated. class ScalaLogic { var service // How to initialize? def setService (srv: OutputService) = { service = srv } Is there a way to initialize the var service so that I can later assign a dependency into it? It should be lexically scoped to be visible in the whole class.

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• django: how to use many-to-many relationships in values()?

  - by john

  i need to group results by a field that requires a few joins from the original model: // response_filter_args is created dynamically responses = Response.objects.filter(**response_filter_args) \ .values('customer__tags__tag') \ # django doesn't like this .annotate(average_score=Avg('rating__score')) Response - customer - tags (many-to-many field pointing to Tag) - tag (the tag as a string) Models are: class Response(models.Model): customer = models.ForeignKey(Customer) ... class Customer(models.Model): tags = models.ManyToManyField(Tag) ... class Tag(models.Model): tag = models.CharField(max_length=255) ... i'm trying to calculate average ratings. to make it work i need to tell django to group by 'tag', but it refuses to. it gives an error: Invalid field name: 'customer__tags__tag' anyone know how i can get it to group by tag? i've tried all the combinations of underscores in customer_tags_tag that i can think of, but nothing works.

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• 1:M relationship in Hibernate and cascading operations

  - by EugeneP

  Table SUBCOURSE references COURSE COURSE(id, name) SUBCOURSE(id, course_id, name) So, 1:M. Hibernate generates for Course: @OneToMany(fetch = FetchType.LAZY, mappedBy = "course", cascade = CascadeType.ALL) public Set getSubCourses() { return this.subCourses; } for Subcourse it generates @ManyToOne(fetch = FetchType.LAZY) @JoinColumn(name = "course_id", nullable = false) public Course getCourse() { return this.course; } Now the problem is that cascading does not work as expected. I want to create a collection of SubCourse objects (Set), fill it and then bind it to setSubCourses() of Course object. Though, having ManyToOne thing in a Subcourses table, I need to manually setCourse() before adding to collection on each object. If I do not do so, an exception is raised. What can you recommend me?

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• Why does `Array.length`, `Function.length`, `String.length`, etc return 1?

  - by zealoushacker

  While teaching my JavaScript class yesterday, my students and I came across some interesting functionality that I thought might be worth capturing in a question and the answer I've come to. Typing Array.length in the JS console in chrome returns 1. Likewise, Function.length returns 1. This is important because: Every function in JavaScript is actually a Function object. (MDN JS Ref: Function) Thus, Object.length and likely all other native objects will and should return 1 as the value of the length property. So, finally why is this behavior occurring?

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• Java: howto write equals() shorter

  - by erikb

  I get headaches when I have to write nearly 10 lines of code to say 2 Objects are equal, when their type is equal and both's attribute is equal. You can easily see that in this way of writing the number of lines increase drastically with your number of attributes. public class Id implements Node { private String name; public Id(String name) { this.name = name; } public boolean equals(Object o) { if (o == null) return false; if (null == (Id) o) return false; Id i = (Id) o; if ((this.name != null && i.name == null) || (this.name == null && i.name != null)) return false; return (this.name == null && i.name == null) || this.name.equals(i.name); } }

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• Create Object using ObjectBuilder

  - by dhinesh

  Want to create objects using ObjectBuilder or ObjectBuilder2. I do not want to use StructureMap I was able to create the object having parameterless constructor using the code mentioned below. public class ObjectFactory : BuilderBase<BuilderStage> { public static T BuildUp<T>() { var builder = new Builder(); var locator = new Locator { { typeof(ILifetimeContainer), new LifetimeContainer() } }; var buildUp = builder.BuildUp<T>(locator, null, null); return buildUp; } for creating object of customer you just call ObjectFactory.BuildUp<Customer> However this creates object of class which has no parameters, however I need to create object which are having constructor with parameters.

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• How does Ruby's Array.| compare elements for equality?

  - by Max Howell

  Here's some example code: class Obj attr :c, true def == that p '==' that.c == self.c end def <=> that p '<=>' that.c <=> self.c end def equal? that p 'equal?' that.c.equal? self.c end def eql? that p 'eql?' that.c.eql? self.c end end a = Obj.new b = Obj.new a.c = 1 b.c = 1 p [a] | [b] It prints 2 objects but it should print 1 object. None of the comparison methods get called. How is Array.| comparing for equality?

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• Sort List based on dynamically generated numbers in C++

  - by user367322

  I have a list of objects ("Move"'s in this case) that I want to sort based on their calculated evaluation. So, I have the List, and a bunch of numbers that are "associated" with an element in the list. I now want to sort the List elements with the first element having the lowest associated number, and the last having the highest. Once the items are order I can discard the associated number. How do I do this? This is what my code looks like (kind've): list<Move> moves = board.getLegalMoves(board.turn); for(i = moves.begin(); i != moves.end(); ++i) { //... a = max; // <-- number associated with current Move }

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