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• Enum.values() vs EnumSet.allOf( ). Which one is more preferable?

  - by Alexander Pogrebnyak

  I looked under the hood for EnumSet.allOf and it looks very efficient, especially for enums with less than 64 values. Basically all sets share the single array of all possible enum values and the only other piece of information is a bitmask which in case of allOf is set in one swoop. On the other hand Enum.values() seems to be a bit of black magic. Moreover it returns an array, not a collection, so in many cases it must be decorated with Arrays.asList( ) to be usable in any place that expects collection. So, should EnumSet.allOf be more preferable to Enum.values? More specifically, which form of for iterator should be used: for ( final MyEnum val: MyEnum.values( ) ); or for ( final MyEnum val: EnumSet.allOf( MyEnum.values ) );

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• Hook Response.Cache to memcache

  - by dvr

  Has anyone done this before? I have a 32 bit win 2003 server running 2.0 and have read the ms engineers' blog about min(60%, 1800mb) for cache limits and our site (asp.net 2.0 / 3.5) is caching alot. It throws system outofmemory exceptions when wp is around 1.3gb (unfortunately it is the 2.0 apps) and I would like to push alot over to memcache but worried that at the moment the site is efficient using response.cache as is (though memory is an issue). I want to move most items over to memcache and have concerns on a – how to do this (implementation of response.cache to read/write from memcache) and b – what will performance be like? Before I commit to doing this and possibly spending a few days running tests I would like to hear from you if this has been done already and get some feedback. (and please don’t tell me to buy a x64 machine – I have already requested this!), by the way I ran a test requesting a single image 1000 times and response.cache was over 50% quicker than using application cache. Does response.cache bypass the page lifecycle?

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• Stochastic calculus library in python

  - by LeMiz

  Hello, I am looking for a python library that would allow me to compute stochastic calculus stuff, like the (conditional) expectation of a random process I would define the diffusion. I had a look a at simpy (simpy.sourceforge.net), but it does not seem to cover my needs. This is for quick prototyping and experimentation. In java, I used with some success the (now inactive) http://martingale.berlios.de/Martingale.html library. The problem is not difficult in itself, but there is a lot non trivial, boilerplate things to do (efficient memory use, variable reduction techniques, and so on). Ideally, I would be able to write something like this (just illustrative): def my_diffusion(t, dt, past_values, world, **kwargs): W1, W2 = world.correlated_brownians_pair(correlation=kwargs['rho']) X = past_values[-1] sigma_1 = kwargs['sigma1'] sigma_2 = kwargs['sigma2'] dX = kwargs['mu'] * X * dt + sigma_1 * W1 * X * math.sqrt(dt) + sigma_2 * W2 * X * X * math.sqrt(dt) return X + dX X = RandomProcess(diffusion=my_diffusion, x0 = 1.0) print X.expectancy(T=252, dt = 1./252., N_simul= 50000, world=World(random_generator='sobol'), sigma1 = 0.3, sigma2 = 0.01, rho=-0.1) Does someone knows of something else than reimplementing it in numpy for example ?

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• Ruby on Rails: Model.all.each vs find_by_sql("SELECT * FROM model").each ?

  - by B_

  I'm fairly new to RoR. In my controller, I'm iterating over every tuple in the database. For every table, for every column I used to call SomeOtherModel.find_by_sql("SELECT column FROM model").each {|x| #etc } which worked fine enough. When I later changed this to Model.all(:select => "column").each {|x| #etc } the loop starts out at roughly the same speed but quickly slows down to something like 100 times slower than the the find_by_sql command. These calls should be identical so I really don't know what's happening. I know these calls are not the most efficient but this is just an intermediate step and I will optimize it more once this works correctly. Thanks!

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• One position right barrel shift using ALU Operators?

  - by Tomek

  I was wondering if there was an efficient way to perform a shift right on an 8 bit binary value using only ALU Operators (NOT, OR, AND, XOR, ADD, SUB) Example: input: 00110101 output: 10011010 I have been able to implement a shift left by just adding the 8 bit binary value with itself since a shift left is equivalent to multiplying by 2. However, I can't think of a way to do this for shift right. The only method I have come up with so far is to just perform 7 left barrel shifts. Is this the only way?

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• php selecting hash using wildcards

  - by tipu

  Say I have a hashmap, $hash = array('fox' => 'some value', 'fort' => 'some value 2', 'fork' => 'some value again); I am trying to accomplish an autocomplete feature. When the user types 'fo', I would like to retrieve, via ajax, the 3 keys from $hash. When the user types 'for', I would like to only retrieve the keys fort and fork. Is this possible? What I was thinking was using binary search to isolate the keys with 'f', instead of brute-force searching. Then continue eliminating the indexes as the user types out their query. Is there a more efficient solution to this?

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• Removing duplicates without overriding hash method

  - by Javi

  Hello, I have a List which contains a list of objects and I want to remove from this list all the elements which have the same values in two of their attributes. I had though about doing something like this: List<Class1> myList; .... Set<Class1> mySet = new HashSet<Class1>(); mySet.addAll(myList); and overriding hash method in Class1 so it returns a number which depends only in the attributes I want to consider. The problem is that I need to do a different filtering in another part of the application so I can't override hash method in this way (I would need two different hash methods). What's the most efficient way of doing this filtering without overriding hash method? Thanks

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• store everything only once, smarter

  - by hsmit

  In the digital world a lot is stored multiple times. As a thought experiment or creative challenge I want you to think about making this more efficient and maybe reuse more. Think of the following cases: an mp3 track is downloaded multiple times, copied over various devices on website a login form is often rebuild many times, why not reuse more code? words themselves are used many times questions and answers are accidentally saved at many places in parallel images or photos often describe the same data (Eiffel tower, Golden gate, Taj Mahal) etc etc Are you aware of solutions? Or are you thinking about similar topics? Ideas? Blueprints? I'd love to hear from you!

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• Must have JavaScript pro developer tools, libs, utilities and workshop configuration.

  - by WooYek

  This is a followup question to the Pro JavaScript programmer interview questions (with answers). What is considered professional and industrial standard for a professional browser side Java Script developer when it comes to his workshop configuration, and maybe from-concept-to-shipment process? What are the most popular IDE's, utilities and probably libraries, not limited to the free ones. These that can help cut development time (eg. IDE), help with achieve better quality (eg. unit testing tools), reliability and maintainability. I'm looking for a baseline to which I could compare potential candidates based on their ability to keep their tools sharp and workshop efficient (pro's should invest time&money in good tools, right?).

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• SqlServer2008 - Can I Alter a Scalar Function while it is referenced in many places

  - by Casey C.

  We have a scalar function that returns a DateTime. It performs a couple of quick table selects to get its return value. This function is already in use throughout the database - in default constraints, stored procs, etc. I would like to change the implementation of the function (to remove the table hits and make it more efficient) but apparently I can't do that while it is referenced by other objects in the database. Will I actually need to update every object in the database that references it to remove the reference, update the function and then update all those objects to restore the reference to the function? Thanks for any insight you can give.

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• Trying to speed up a SQLITE UNION QUERY

  - by user142683

  I have the below SQLITE code SELECT x.t, CASE WHEN S.Status='A' AND M.Nomorebets=0 THEN S.PriceText ELSE '-' END AS Show_Price FROM sb_Market M LEFT OUTER JOIN (select 2010 t union select 2020 t union select 2030 t union select 2040 t union select 2050 t union select 2060 t union select 2070 t ) as x LEFT OUTER JOIN sb_Selection S ON S.MeetingId=M.MeetingId AND S.EventId=M.EventId AND S.MarketId=M.MarketId AND x.t=S.team WHERE M.meetingid=8051 AND M.eventid=3 AND M.Name='Correct Score' With the current interface restrictions, I have to use the above code to ensure that if one selection is missing, that a '-' appears. Some feed would be something like the following SelectionId Name Team Status PriceText =================================== 1 Barney 2010 A 10 2 Jim 2020 A 5 3 Matt 2030 A 6 4 John 2040 A 8 5 Paul 2050 A 15/2 6 Frank 2060 S 10/11 7 Tom 2070 A 15 Is using the above SQL code the quickest & efficient?? Please advise of anything that could help. Messages with updates would be preferable.

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• Comparing multiple entity properties against list of entities

  - by roosteronacid

  Consider this snippet of code: var iList = new List<Entities.Ingredient> { new Entities.Ingredient { Name = "tomato", Amount = 2.0 }, new Entities.Ingredient { Name = "cheese", Amount = 100.0 } }; var matches = new DataContext().Ingredients.Where(i => Comparer(i, iList)); private Boolean Comparer(Entities.Ingredient i, List<Entities.Ingredient> iList) { foreach (var i in iList) { if (i.Name == iList.Name && i.Amount >= iList.Amount) return true; } return false; } Is there a more efficient way of doing this? Preferably without being too verbose; from x in y select z... If thats at all possible.

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• Web Services: more frequent "small" calls, or less frequent "big" calls

  - by Klay

  In general, is it better to have a web application make lots of calls to a web service getting smaller chunks of data back, or to have the web app make fewer calls and get larger chunks of data? In particular, I'm building a Silverlight app that needs to get large amounts of data back from the server in response to a query created by a user. Each query could return anywhere from a few hundred records to a few thousand. Each record has around thirty fields of mostly decimal-type data. I've run into the situation before where the payload size of the response exceeded the maximum allowed by the service. I'm wondering whether it's better (more efficient for the server/client/web service) to cut this payload vertically--getting all values for a single field with each call--or horizontally--getting batches of complete records with each call. Or does it matter?

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• Instantiating a context in LINQ to Entities

  - by Jagd

  I've seen two different manners that programmers approach when creating an entity context in their code. The first is like such, and you can find it all over the MSDN code examples: public void DoSomething() { using TaxableEducationEntities context = new TaxableEducationEntities()) { // business logic and whatever else } } The second is to create the context as a private attribute in some class that encapsulates your business logic. So you would have something like: public class Education_LINQ { private TaxableEducationEntities context = new TaxableEducationEntities(); public void DoSomething() { var result = from a in context.luAction select a; // business logic and whatever else } } Which way is more efficient? Assume that you have two methods, one called DoSomething1() and another called DoSomething2(), and both methods incorporate the using statement to open the context and do whatever with it. Were you to call one method after the other, would there be any superfluous overhead going on, since essentially both methods create the context and then clean it up when they're done? As opposed to having just one private attribute that is created when a class object is instantiated, and then in turn cleaned up when the object goes out of scope?

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• MySQL index cardinality - performance vs storage efficiency

  - by Sean

  Say you have a MySQL 5.0 MyISAM table with 100 million rows, with one index (other than primary key) on two integer columns. From my admittedly poor understanding of B-tree structure, I believe that a lower cardinality means the storage efficiency of the index is better, because there are less parent nodes. Whereas a higher cardinality means less efficient storage, but faster read performance, because it has to navigate through less branches to get to whatever data it is looking for to narrow down the rows for the query. (Note - by "low" vs "high", I don't mean e.g. 1 million vs 99 million for a 100 million row table. I mean more like 90 million vs 95 million) Is my understanding correct? Related question - How does cardinality affect write performance?

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• How do I regenerate statistics in Openx?

  - by Martin Bauer

  ue to faulty hardware, statistics generated over a 2 week period were significantly higher than normal (10000 times higher than normal). After moving the application to a new server, the problem rectified itself. The issue I have is that there are 2 weeks of stats that are clearly wrong. I have checked the raw impressions table for the affected fortnight and it seems to be correct (ie. stats per banner per day match the average for the previous month). Looking at the intermediate & summary impressions tables, the values are inflated. I understand from the openx forum (http://forum.openx.org/index.php?s=7796fd9dae40e020a010773746f3ada9&showtopic=503424297) it's possible to regenerate stats from the raw data but it will only regenerate stats per hour, meaning regenerating stats for 2 weeks would be very time consuming. Is there another, more efficient way to regenerate the stats from the raw data for the affected fortnight?

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• Best strategy for HTML partial rendering based on multiple dropdown values

  - by pv2008

  I have a View that renders something like this: "Item 1" and "Item 2" are <tr> elements from a table. After the user change "Value 1" or "Value 2" I would like to call a Controller and put the result (some HTML snippet) in the div marked as "Result of...". I have some vague notions of JQuery. I know how to bind to the onchange event of the Select element, and call the $.ajax() function, for example. But I wonder if this can be achieved in a more efficient way in ASP.NET MVC2.

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• Difference b/w putting condition in JOIN clause versus WHERE clause

  - by user244953

  Suppose I have 3 tables. Sales Rep Rep Code First Name Last Name Phone Email Sales Team Orders Order Number Rep Code Customer Number Order Date Order Status Customer Customer Number Name Address Phone Number I want to get a detailed report of Sales for 2010. I would be doing a join. I am interested in knowing which of the following is more efficient and why ? SELECT O.OrderNum, R.Name, C.Name FROM Order O INNER JOIN Rep R ON O.RepCode = R.RepCode INNER JOIN Customer C ON O.CustomerNumber = C.CustomerNumber WHERE O.OrderDate >= '01/01/2010' OR SELECT O.OrderNum, R.Name, C.Name FROM Order O INNER JOIN Rep R ON (O.RepCode = R.RepCode AND O.OrderDate >= '01/01/2010') INNER JOIN Customer C ON O.CustomerNumber = C.CustomerNumber

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• PHP Special Characters Test

  - by pws5068

  What's an efficient way of checking if a username contains a number of special characters that I define. Examples: % # ^ . ! @ & ( ) + / " ? ` ~ < { } [ ] | = - ; I need to detect them and return a boolean, not just strip them out. Probably a super easy question but I need a better way of doing this than a huge list of conditionals or a sloppy loop.

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• OpenLayers, Layers: Tiled vs. single tile

  - by Chau

  Each time we add a new layer to our OpenLayers based website (data provided primarily by a GeoServer server), we discuss whether to use a single-tile or a tiled approach. Some of the parameters we evaluate are the following: Using the tiled approach we get: Slow but continuous buildup of the viewport Lots of small images Client side caching possibilities Blocking of the loading pipeline (6 requests at a time) Jerky feeling when navigating during load Using the single-tile approach we get: Smoother feeling when navigating during load Time delay before layer is loaded One large image for each layer No caching of the single tile We have a lot of data editing in the layers, thus a tile-cache might not be that efficient. Are there any best-practices when it comes to tiling? Progressing towards infinitely fast hardware and unlimited data connections, the discussion becomes irrelevant, but what configuration do you percieve as the most user-pleasing?

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• effective retrieve for a voting system in PHP and MySQL

  - by Adnan

  Hello, I have a system where registered users can vote up/vote down comment for a picture. Something very similar to SO's voting system. I store the votes in a table with values as such; vote_id | vote_comment_id | vote_user_id | vote_date | vote_type Now I have few a question concerned the speed and efficiency for the following; PROB: Once a user opens the picture page with comments I need, if that user has already voted UP/DOWN a comment to show it like; "you voted up" or "you voted down" next to the comment (in SO it the vote image is highlighted) MY POSSIBLE SOL: Right now when I open a picture page for each comment I loop thru, I loop thru my table of votes as well and check if a user has voted and show the status (I compare the vote_user_id with the user's session). How efficient is this? Anyone have a better approach to tackle this kind of problem?

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• jQuery parent of a parent

  - by Bloudermilk

  Hello, I am currently trying to find the parent of a parent of an element. I have a link being clicked that is in a <td>, and I'd like to get the <tr> object. Why wont "$(this).parent().parent()" work? What will? Thanks, Brendan Edit: It appears an error in my syntax was throwing the whole thing off. "$(this).parent().parent()" does in fact work, but I wound up going with $(this).closest('tr')" because it seems like the most efficient solution.

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• Multilangual Unicode rendering in opengl

  - by sum1stolemyname

  Hi Folks, I have to extend an OpenGL-Rendering System to support international characters (especially Hebrew, Arabic and cyrillic). Development Platform is Windows(XP|Vista|7), Alas using Embercardero Delphi 2010. I currently use wglOutLineFont(...) to build my font's display list and glCallLists(length(m_Text), UNSIGNED_SHORT, PWchar(m_Text) ) to render my strings. While this is feasable for Latin-1 Characters, building the full unicode character set in advanced is pretty time-consuming (about 8.5 minutes on my machine), so i am looking for a more efficient solution. I thought about limiting the range from u+0020 - u+077f (latin, greek, cyrillic, arbaic and hebrew) to include just the glyphs i need, but that would just be a solution for my current needs, and will become insufficent once other encoding is needed. On the upside, i do not have to worry about left-to right or right-to left direction as our application can handle this already. I would expect this to be a well-known problem, so i would like to ask if there is any reference material on this on the web, or if you could share some insight on this?

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• How to rotate an SSE/AVX vector

  - by user1584773

  I need to perform a rotate operation with as little clock cycle as possible. In the first case let's assume __m128i as source and dest type source: || A0 || A1 || A2 || A3 || dest : || A1 || A2 || A3 || A0 || dest = (__m128i)_mm_shuffle_epi32((__m128i)source, _MM_SHUFFLE(0,3,2,1)); Now I want to do the same whit AVX intrinsics So let's assume this time __m256i as source and dest type source: || A0 || A1 || A2 || A3 || A4 || A5 || A6 || A7 || dest : || A1 || A2 || A3 || A4 || A5 || A6 || A7 || A0 || The Avx intrinsics is missing most of the corresponding SSE integer operations. Maybe there is some way go get the desider output working with the floating point version. I've tryed with: dest = (__m256i)_mm256_shuffle_ps((__m256)source, (__m256)source, _MM_SHUFFLE(0,3,2,1)); but what I get is: || A0 || A2 || A3 || A4 || A5 || A6 || A7 || A1 || Any Idea on how to solve this in an efficient way? (without mixing SSE and AVX operation and without "manually" inverting A0 and A1 Thanks in advance!

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• Auto refresh web page

  - by Epitaph

  I have a web page which allows the user to carry out various operations that in turn modify the database. Also, this web application needs to keep track of various fields in database that keep changing with time. Is refreshing the page every few seconds the best possible way to implement this? For example, if there is a long list on the page requiring scrolling, it is hard to view the list since the page keeps resetting due to the refresh. I know, there are ways to retain the position of the scroll. But, could I use something more efficient?

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