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• Java string to double conversion.

  - by wretrOvian

  Hi, I've been reading up on the net about the issues with handling float and double types in java. Unfortunately, the image is still not clear. Hence, i'm asking here direct. :( My MySQL table has various DECIMAL(m,d) columns. The m may range from 5 to 30. d stays a constant at 2. Question 1. What equivalent data-type should i be using in Java to work (i.e store, retrieve, and process) with the size of the values in my table? (I've settled with double - hence this post). Question 2. While trying to parse a double from a string, i'm getting errors Double dpu = new Double(dpuField.getText()); for example - "1" -> java.lang.NumberFormatException: empty String "10" -> 1.0 "101" -> 10.0 "101." -> 101.0 "101.1" -> 101.0 "101.19" -> 101.1 What am i doing wrong? What is the correct way to convert a string to a double value? And what measures should i take to perform operations on such values?

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• scheme basic loop

  - by utku

  I'm trying to write a scheme func that behaves in a way similar to a loop. (loop min max func) This loop should perform the func between the range min and max (integers) -- one of an example like this (loop 3 6 (lambda (x) (display (* x x)) (newline))) 9 16 25 36 and I define the function as ( define ( loop min max fn) (cond ((>= max min) ( ( fn min ) ( loop (+ min 1 ) max fn) ) ) ) ) when I run the code I get the result then an error occur. I couldn't handle this error. (loop 3 6 (lambda (x) (display(* x x))(newline))) 9 16 25 36 Backtrace: In standard input: 41: 0* [loop 3 6 #] In utku1.scheme: 9: 1 (cond ((= max min) ((fn min) (loop # max fn)))) 10: 2 [# ... 10: 3* [loop 4 6 #] 9: 4 (cond ((= max min) ((fn min) (loop # max fn)))) 10: 5 [# ... 10: 6* [loop 5 6 #] 9: 7 (cond ((= max min) ((fn min) (loop # max fn)))) 10: 8 [# ... 10: 9* [loop 6 6 #] 9: 10 (cond ((= max min) ((fn min) (loop # max fn)))) 10: 11 [# #] utku1.scheme:10:31: In expression ((fn min) (loop # max ...)): utku1.scheme:10:31: Wrong type to apply: #<unspecified> ABORT: (misc-error)

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• Why I can't get all UDP packets?

  - by Jack

  My program use UdpClient to try to receive 27 responses from 27 hosts. The size of the response is 10KB. My broadband incoming bandwidth is 150KB/s. The 27 responses are sent from the hosts almost at the same time and for every 10 secs. However, I can only receive 8 - 17 responses each time. The number of responses that I can receive is quite dynamic but within the range. Can anyone tell me why? why can't I receive all? I understand UDP is not reliable. but I tried receiving 5 - 10 responses at the same time, it worked. I guess the network links are not so bad. The code is very simple. ON the 27 hosts, I just use UdpClient to send 10KB to my machine. On my machine, I have one UdpClient receive datagrams. Each time I get a data, I create a thread to handle it (basically handling it means just print out "I received 10KB", but it runs in a thread). listener = new UDPListener(Port); listener.Start(); while (true) { try { UDPContext context = listener.Accept(); ThreadPool.QueueUserWorkItem(new WaitCallback(HandleMessage), context); } catch (Exception) { } } If I reduce the size of the response down to 3KB, the case gets much better that roughly 25 responses can be received. Any more idea? UDP buffer problems???

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• WCF data services - Limiting related objects returned based on critera

  - by Mike Morley

  I have an object graph consisting of a base employee object, and a set of related message objects. I am able to return the employee objects based on search criteria on the employee properties (eg team) etc. However, if I expand on the messages, I get the full collection of messages back. I would like to be able to either take the top n messages (i.e. restrict to 10 most recent) or ideally use a date range on the message objects to limit how many are brought back. So far I have not been able to figure out a way of doing this: I get an error if I attempt to filter on properties on the message (&$filter=employee/message/StartDate gives an error "No property 'StartDate' exists in type 'System.Data.Objects.DataClasses.EntityCollection`1). Attempting to use Top on the message related object doesn't work either. I have also tried using a WebGet extension that takes a string list of employee IDs. That works until the list gets too long, and then fails due to the URL getting too long (it might be possible to setup a paging mechanism on this approach)... Unfortunately the UI control I am using requires the data to be in a fairly specific hierarchical shape, so I can't easily come at this from starting on the message side and working backwards. Outside of making multiple calls does anyone know of a method to accomplish this with wcf data services? Thanks! M.

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• Screenscraping and reverse engineering health based web tool

  - by ArbInv

  Hi There is a publicly available free tool which has been built to help people understand the impact of various risk factors on their health / life expectancy. I am interested in understanding the data that sits behind the tool. To get this out it would require putting in a range of different socio-demographic factors and analyzing the resulting outputs. This would need to be done across many thousand different individual profiles. The tool was probably built on some standard BI platorm. I have no interest in how the tool was built but do want to get to the data within it. The site has a Terms of Use Agreement which includes: Not copying, distribute, adapt, create derivative works of, translate, or otherwise modify the said tool Not decompile, disassemble, reverse assemble, or otherwise reverse engineer the tool. The said institution retains all rights, title and interest in and to the Tool, and any and all modifications thereof, including all copyright, copyright registrations, trade secrets, trademarks, goodwill and confidential and proprietary information related thereto. Would i be in effect breaking the law if i were to point a screen scraping tool which downloaded the data that sits behind the tool in question?? Any advice welcomed? THANKS

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• WCF with MANY database connections

  - by Jorge Dominguez

  I'm working in the development of an ERP type .Net WinForms application consuming a WCF service. It's to be used by many small companies (in the range of 100-200). Database is SQL Server 2008 and the service will be hosted as a Windows service. Even thought there will be a single DB Server, our customer insists in having separate databases for each company. That is because of stability/support concerns (like DB being damaged or took offline for some reason thus affecting all clients). Concerns coming from previous experiences (not necessarily with same platform). With a single database, connections to the DB would be opened at service start up and pooling used, but, I'm not sure how connections could be managed in a multiple DB scenario: Could a connection to the corresponding DB be opened and closed for each service request? would performance be acceptable? If a connection is opened and maintained for each company accessing the system, what's the practical limit of opened connections (to different databases)? It would be very interesting to hear your opinions and suggestions for this situation. Tanks

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• Twitter Favorites and more than 20

  - by danit

  Im using curl to fetch my Twitter favorites: <?php $username = "bob"; $password = "password"; $twitterHost = "http://twitter.com/favorites.xml"; $curl; $curl = curl_init(); curl_setopt($curl, CURLOPT_CONNECTTIMEOUT, 2); curl_setopt($curl, CURLOPT_HEADER, false); curl_setopt($curl, CURLOPT_HTTPAUTH, CURLAUTH_BASIC); curl_setopt($curl, CURLOPT_RETURNTRANSFER, 1); curl_setopt($curl, CURLOPT_USERPWD, "$username:$password"); curl_setopt($curl, CURLOPT_HTTP_VERSION, CURL_HTTP_VERSION_1_1); curl_setopt($curl, CURLOPT_URL, $twitterHost); $result = curl_exec($curl); curl_close($curl); header('Content-Type: application/xml; charset=ISO-8859-1'); print $result; ?> However this only fetches the last 20 favorites, not all of them. If i amend this line: $twitterHost = "http://twitter.com/favorites.xml"; And change it to: $twitterHost = "http://twitter.com/favorites.xml?page=2"; I can get the next set of 20 favorites. There doesnt appear to be anyway, using the Twitter API, to find out how many pages of favorites there are. As such can anyone suggest the best way to get all favorites? Or if this is not possible, get all the Tweets for a date range?

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• Dynamically disable custom (VBA) Excel context menu buttons?

  - by Lopsided

  The Scenario Hi guys, I am about to add a few custom controls to the cell context menu in my Excel workbook using the instructions found on this MSDN page. The only problem I am having is that I need the items to only be enabled for a specific column/range of cells. I've looked around, and I've been unable to find any steps for this--there are some for VSTO development (written in C#), but that is not what I need. I plan to write this using the VBA IDE built into Office, and perhaps a bit of XML using the Custom UI Editor. The Question So basically, I'm looking for a way to run a function at the time the context menu is called (i.e., upon right-click) that validates the selection to make sure it is in the appropriate column. If it isn't, I would like my custom buttons to be greyed out. P.S. Please don't think I am asking you to write my code. Creating these buttons should be very simple, as I have created many before (albeit they were all Ribbon items), and I hope it is okay to ask for some quick assistance on this very specific issue. Thank you in advance!

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• Calling NSFetchedResultsController & CoreData experts

  - by JK

  I am having a few nagging issues with NSFetchedResultsController and CoreData, any of which I would be very grateful to get help on. Issue 1 - Updates: I update my store on a background thread which results in certain rows being delete, inserted or updated. The changes are merged into the context on the main thread using the "mergeChangesFromContextDidSaveNotification:" method. Inserts and deletes are updated properly, but updates are not (e.g. the cell label is not updated with the change) although I have confirmed the updates to come through the contextDidSaveNotifcation, exactly like the inserts and deleted. My current workaround is to temporarily change the staleness interval of the context to 0, but this does not seem like the ideal solution. Issue 2 - Deleting objects: My fetch batch size is 20. If an object is deleted by the background thread which is in the first 20 rows, everything works fine. But if the object is after the first 20 rows and the table is scrolled down, a "CoreData could not fulfill a fault" error is raised. I have tried resaving the context and reperforming the frc fetch - all to no avail. Note: In this scenario, the frc delegate method "didChangeObject...." is not called for the delete - I assume this is because the object in question had not been faulted at that time (as it is was outside the initial fetch range). But for some reason, the context still thinks the object is around, although is has been deleted from the store. Issue 3 - Deleting sections : When the deletion of a row leads to the deletion of a section, I have gotten the "invalid number of rows in section???" error. I have worked around this by removing the "reloadSection" line from the NSFetchedResultsChangeMove: section and replacing it with "[tableView insertRowsAtIndexPaths...." This seems to work, but once again, I am not sure if this is the best solution. Any help would be greatly appreciated. Thank you!

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• How to R/W hard disk when CPU is in Protect Mode?

  - by smwikipedia

  I am doing some OS experiment. Until now, all my code utilized the real mode BIOS interrupt to manipulate hard disk and floppy. But once my code enabled the Protect Mode of the CPU, all the real mode BIOS interrupt service routine won't be available. How could I R/W the hard disk and floppy? I have a feeling that I need to do some hardware drivers now. Am I right? Is this why an OS is so difficult to develop? I know that hardwares are all controlled by reading from and writing to certain control or data registers. For example, I know that the Command Block Registers of hard disk range from 0x1F0 to 0x1F7. But I am wondering whether the register addresses of so many different hardwares are the same on the PC platform? Or do I have to detect that before using them? How to detect them?? For any responses I present my deep appreciation.

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• How to do "map chunks", like terraria or minecraft maps?

  - by O'poil

  Due to performance issues, I have to cut my maps into chunks. I manage the maps in this way: listMap[x][y] = new Tile (x,y); I tried in vain to cut this list for several "chunk" to avoid loading all the map because the fps are not very high with large map. And yet, when I update or Draw I do it with a little tile range. Here is how I proceed: foreach (List<Tile> list in listMap) { foreach (Tile leTile in list) { if ((leTile.Position.X < screenWidth + hero.Pos.X) && (leTile.Position.X > hero.Pos.X - tileSize) && (leTile.Position.Y < screenHeight + hero.Pos.Y) && (leTile.Position.Y > hero.Pos.Y - tileSize) ) { leTile.Draw(spriteBatch, gameTime); } } } (and the same thing, for the update method). So I try to learn with games like minecraft or terraria, and any two manages maps much larger than mine, without the slightest drop of fps. And apparently, they load "chunks". What I would like to understand is how to cut my list in Chunk, and how to display depending on the position of my character. I try many things without success. Thank you in advance for putting me on the right track! Ps : Again, sorry for my English :'( Pps : I'm not an experimented developer ;)

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• How to store and locate multiple interface types within a Delphi TInterfaceList

  - by Brian Frost

  Hi, I'm storing small interfaces from a range of objects into a single TInterfaceList 'store' with the intention of offering list of specific interface types to the end user, so each interface will expose a 'GetName' function but all other methods are unique to that interface type. For example here are two interfaces: IBase = interface //---------------------------------------- function GetName : string; //---------------------------------------- end; IMeasureTemperature = interface(IBase) //------------------------------------ function MeasureTemperature : double; //---------------------------------------- end; IMeasureHumidity = interface(IBase) //---------------------------------------- function MeasureHumidity: double; //---------------------------------------- end; I put several of these interfaces into a single TInterfaceList and then I'd like to scan the list for a specific interface type (e.g. 'IMeasureTemperature') building another list of pointers to the objects exporting those interfaces. I wish to make no assumptions about the locations of those objects, some may export more than one type of interface. I know I could do this with a class hierarchy using something like: If FList[I] is TMeasureTemperature then .. but I'd like to do something simliar with an interface type, Is this possible?

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• ArgumentOutOfRangeException was unhandled by user code - (ASP .net)

  - by ASr..

  I use a GridView to display the records from the database. Also i've attached a Hyperlink to the GridView using TemplateField. When I try to add "onclick" attribute to the HyperLink inside the RowDateBound event, I get the following error.. GridView1.DataKeys[e.Row.RowIndex].Value = 'GridView1.DataKeys[e.Row.RowIndex]' threw an exception of type 'System.ArgumentOutOfRangeException' Message = "Index was out of range. Must be non-negative and less than the size of the collection.\r\nParameter name: index" This is the coding inside the RowDataBound mentod.. protected void GridView1_RowDataBound(object sender, GridViewRowEventArgs e) { if (e.Row.RowType == DataControlRowType.DataRow) { HyperLink HyperLink1 = (HyperLink)e.Row.FindControl("HyperLink1"); //The following line makes the error HyperLink1.Attributes.Add("onclick", "ShowMyModalPopup('" + GridView1.DataKeys[e.Row.RowIndex].Value + "')"); } } This is "ShowMyModalPopup" function in javascript <script type="text/javascript"> function ShowMyModalPopup(userpk) { var modal = $find('ModalPopupExtender1'); modal.show(); WebService.FetchOneUser(userpk,DisplayResult); } </script> Can anyone please explain me why this error occurs.. Many thanks in advance..

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• Data structure to build and lookup set of integer ranges

  - by actual

  I have a set of uint32 integers, there may be millions of items in the set. 50-70% of them are consecutive, but in input stream they appear in unpredictable order. I need to: Compress this set into ranges to achieve space efficient representation. Already implemented this using trivial algorithm, since ranges computed only once speed is not important here. After this transformation number of resulting ranges is typically within 5 000-10 000, many of them are single-item, of course. Test membership of some integer, information about specific range in the set is not required. This one must be very fast -- O(1). Was thinking about minimal perfect hash functions, but they do not play well with ranges. Bitsets are very space inefficient. Other structures, like binary trees, has complexity of O(log n), worst thing with them that implementation make many conditional jumps and processor can not predict them well giving poor performance. Is there any data structure or algorithm specialized in integer ranges to solve this task?

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• Collision detection problems...

  - by thyrgle

  Hi, I have written the following: -(void) checkIfLineCollidesWithAll { float slope = ((160-L1Circle1.position.y)-(160-L1Circle2.position.y))/((240-L1Circle1.position.x)-(240-L1Circle2.position.x)); float b = (160-L1Circle1.position.y) - slope * (240-L1Circle1.position.x); if ((240-L1Sensor1.position.x) < (240-L1Circle1.position.x) && (240-L1Sensor1.position.x) < (240-L1Circle2.position.x) || ((240-L1Sensor1.position.x) > (240-L1Circle1.position.x) && (240-L1Sensor1.position.x) > (240-L1Circle2.position.x))) { [L1Sensor1 setTexture:[[CCTextureCache sharedTextureCache] addImage:@"SensorOk.png"]]; } else if (slope == INFINITY || slope == -INFINITY) { if (L1Circle1.position.y + 16 >= L1Sensor1.position.y || L1Circle1.position.y - 16 <= L1Sensor1.position.y) { [L1Sensor1 setTexture:[[CCTextureCache sharedTextureCache] addImage:@"SensorBad.png"]]; } else { [L1Sensor1 setTexture:[[CCTextureCache sharedTextureCache] addImage:@"SensorOk.png"]]; } } else if (160-L1Sensor1.position.y + 12 >= slope*(240-L1Sensor1.position.x) + b && 160-L1Sensor1.position.y - 12 <= slope*(240-L1Sensor1.position.x) + b) { [L1Sensor1 setTexture:[[CCTextureCache sharedTextureCache] addImage:@"SensorBad.png"]]; } else { [L1Sensor1 setTexture:[[CCTextureCache sharedTextureCache] addImage:@"SensorOk.png"]]; } } Basically what this does is finds m and b in the well known equation: y = mx + b and then substitutes coordinates of the L1Sensor1 (the circle I'm trying to detect if it it intersects with the line segment) to see if y = mx + b hold true. But, there are two problems, first, when slope approaches infinity the range of what the L1Sensor1 should "react" to (it "reacts" by changing its image) becomes smaller. Also, the code that should handle infinity is not working. Thanks for the help in advanced.

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• Slow T-SQL query, convert to LINQ to Object

  - by yimbot

  I have a T-SQL query which populates a DataSet from an MSSQL database. string qry = "SELECT * FROM EvnLog AS E WHERE TimeDate = (SELECT MAX(TimeDate) From EvnLog WHERE Code = E.Code) AND (Event = 8) AND (TimeDate BETWEEN '" + Start + "' AND '" + Finish + "')" The database is quite large and being the type of nested query it is, the Data Adapter can take a number of minutes to fill the DataSet. I have extended the DataAdapter's timeout value to 480 seconds to combat it, but the client still complains about slow performance and occassional timeouts. To combat this, I was considering executing a simpler query (ie. just taking the date range) and then populating a Generic List which I could then execute a Linq query against. The simple query executes very quickly which is great. However, I cannot seem to build a Linq query which generates the same results as the T-SQL query above. Is this the best solution to this problem? Can anyone provide tips on rewriting the above T-SQL into Linq? I have also considered using a DataView, but cannot seem to get the results from that either.

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• Paginating requests to an API

  - by user332912

  I'm consuming (via urllib/urllib2) an API that returns XML results. The API always returns the total_hit_count for my query, but only allows me to retrieve results in batches of, say, 100 or 1000. The API stipulates I need to specify a start_pos and end_pos for offsetting this, in order to walk through the results. Say the urllib request looks like "http://someservice?query='test'&start_pos=X&end_pos=Y". If I send an initial 'taster' query with lowest data transfer such as http://someservice?query='test'&start_pos=1&end_pos=1 in order to get back a result of, for conjecture, total_hits = 1234, I'd like to work out an approach to most cleanly request those 1234 results in batches of, again say, 100 or 1000 or... This is what I came up with so far, and it seems to work, but I'd like to know if you would have done things differently or if I could improve upon this: hits_per_page=1000 # or 1000 or 200 or whatever, adjustable total_hits = 1234 # retreived with BSoup from 'taster query' base_url = "http://someservice?query='test'" startdoc_positions = [n for n in range(1, total_hits, hits_per_page)] enddoc_positions = [startdoc_position + hits_per_page - 1 for startdoc_position in startdoc_positions] for start, end in zip(startdoc_positions, enddoc_positions): if end total_hits: end = total_hits print "url to request is:\n ", print "%s&start_pos=%s&end_pos=%s" % (base_url, start, end) p.s. I'm a long time consumer of StackOverflow, especially the Python questions, but this is my first question posted. You guys are just brilliant.

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• Client Side Only Cookies

  - by Mike Jones

  I need something like a cookie, but I specifically don't want it going back to the server. I call it a "client side session cookie" but any reasonable mechanism would be great. Basically, I want to store some data encrypted on the server, and have the user type a password into the browser. The browser decrypts the data with the password (or creates and encrypts the data with the password) and the server stores only encrypted data. To keep the data secure on the server, the server should not store and should never receive the password. Ideally there should be a cookie session expiration to clean up. Of course I need it be available on multiple pages as the user walks through the web site. The best I can come up with is some sort of iframe mechanism to store the data in javascript variables, but that is ugly. Does anyone have any ideas how to implement something like this? FWIW, the platform is ASP.NET, but I don't suppose that matters. It needs to support a broad range of browsers, including mobile. In response to one answer below, let me clarify. My question is not how to achieve the crypto, that isn't a problem. The question is where to store the password so that it is persistent from page to page, but not beyond a session, and in such a way that the server doesn't see it.

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• Use CSS3 nth-child to alternate the float of images within DIV tags...

  - by Aaron Rodgers

  Basically, what I'm trying to create is a page of div tags, each has an image inside them and I'm trying to use CSS3's nth-child to alternate the float of that specific image. But for the life of me, I can't get the nth-child to locate those images. Here is my code so far... CSS .featureBlock img:nth-of-type(even) { float: left; } .featureBlock img:nth-of-type(odd) { float: right; } This is the HTML of one of those div tags.... <div class="featureBlock"> <h1>Multisize Players</h1> <div class="featureHelpBlock"><a href="#">More help with this</a></div> <img src="http://office2.vzaar.com/images/features/ft_multisize_players.png"> <span class="featureContent"><p>A variety of player sizes is important as we recognise the fact that no two videos or websites are ever the same and you will want something that suits your site&#8217;s look. So if you record your video in 4x3 (not widescreen) or 16x9 (widescreen) we have the range of player sizes to suit your exact needs.</p> <p>We encode the video at the time of uploading in the size that you choose so that the picture and sound quality is retained throughout. Users can choose from the following sizes:</p></span> <br style="clear:both"> </div> Hope this makes sense...

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• How to test a Grails Service that utilizes a criteria query (with spock)?

  - by user569825

  I am trying to test a simple service method. That method mainly just returns the results of a criteria query for which I want to test if it returns the one result or not (depending on what is queried for). The problem is, that I am unaware of how to right the corresponding test correctly. I am trying to accomplish it via spock, but doing the same with any other way of testing also fails. Can one tell me how to amend the test in order to make it work for the task at hand? (BTW I'd like to keep it a unit test, if possible.) The EventService Method public HashSet<Event> listEventsForDate(Date date, int offset, int max) { date.clearTime() def c = Event.createCriteria() def results = c { and { le("startDate", date+1) // starts tonight at midnight or prior? ge("endDate", date) // ends today or later? } maxResults(max) order("startDate", "desc") } return results } The Spock Specification package myapp import grails.plugin.spock.* import spock.lang.* class EventServiceSpec extends Specification { def event def eventService = new EventService() def setup() { event = new Event() event.publisher = Mock(User) event.title = 'et' event.urlTitle = 'ut' event.details = 'details' event.location = 'location' event.startDate = new Date(2010,11,20, 9, 0) event.endDate = new Date(2011, 3, 7,18, 0) } def "list the Events of a specific date"() { given: "An event ranging over multiple days" when: "I look up a date for its respective events" def results = eventService.listEventsForDate(searchDate, 0, 100) then: "The event is found or not - depending on the requested date" numberOfResults == results.size() where: searchDate | numberOfResults new Date(2010,10,19) | 0 // one day before startDate new Date(2010,10,20) | 1 // at startDate new Date(2010,10,21) | 1 // one day after startDate new Date(2011, 1, 1) | 1 // someday during the event range new Date(2011, 3, 6) | 1 // one day before endDate new Date(2011, 3, 7) | 1 // at endDate new Date(2011, 3, 8) | 0 // one day after endDate } } The Error groovy.lang.MissingMethodException: No signature of method: static myapp.Event.createCriteria() is applicable for argument types: () values: [] at myapp.EventService.listEventsForDate(EventService.groovy:47) at myapp.EventServiceSpec.list the Events of a specific date(EventServiceSpec.groovy:29)

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• Extended slice that goes to beginning of sequence with negative stride

  - by recursive

  Bear with me while I explain my question. Skip down to the bold heading if you already understand extended slice list indexing. In python, you can index lists using slice notation. Here's an example: >>> A = list(range(10)) >>> A[0:5] [0, 1, 2, 3, 4] You can also include a stride, which acts like a "step": >>> A[0:5:2] [0, 2, 4] The stride is also allowed to be negative, meaning the elements are retrieved in reverse order: >>> A[5:0:-1] [5, 4, 3, 2, 1] But wait! I wanted to see [4, 3, 2, 1, 0]. Oh, I see, I need to decrement the start and end indices: >>> A[4:-1:-1] [] What happened? It's interpreting -1 as being at the end of the array, not the beginning. I know you can achieve this as follows: >>> A[4::-1] [4, 3, 2, 1, 0] But you can't use this in all cases. For example, in a method that's been passed indices. My question is: Is there any good pythonic way of using extended slices with negative strides and explicit start and end indices that include the first element of a sequence? This is what I've come up with so far, but it seems unsatisfying. >>> A[0:5][::-1] [4, 3, 2, 1, 0]

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• .Net Hash Codes no longer persistent?

  - by RobV

  I have an API where various types have custom hash codes. These hash codes are based on getting the hash of a string representation of the object in question. Various salting techniques are used so that as far as possible Hash Codes do not collide and that Objects of different types with equivalent string representations have different Hash Codes. Obviously since the Hash Codes are based on strings there are some collisions (infinite strings vs the limited range of 32 bit integers). I use hashes based on string representations since I need the hashes to persist over sessions and particularly for use in database storage of objects. Suddenly today my code has started generating different hash codes for Objects which is breaking all kinds of things. It was working earlier today and I haven't touched any of the code involved in Hash Code generation. I'm aware that the .Net documentation allows for implementation of hash codes between .Net framework versions to change (and between 32 and 64 bit versions) but I haven't changed the framework version and there has been no framework updates recently as far as I can remember Any ideas because this seems really weird? Edit Hash Codes are generated like follows: //Compute Hash Code this._hashcode = (this._nodetype + this.ToString() + PlainLiteralHashCodeSalt).GetHashCode();

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• Index question: Select * with WHERE clause. Where and how to create index

  - by Mestika

  Hi, I’m working on optimizing some of my queries and I have a query that states: select * from SC where c_id ="+c_id” The schema of ** SC** looks like this: SC ( c_id int not null, date_start date not null, date_stop date not null, r_t_id int not null, nt int, t_p decimal, PRIMARY KEY (c_id, r_t_id, date_start, date_stop)); My immediate bid on how the index should be created is a covering index in this order: INDEX(c_id, date_start, date_stop, nt, r_t_id, t_p) The reason for this order I base on: The WHERE clause selects from c_id thus making it the first sorting order. Next, the date_start and date_stop to specify a sort of “range” to be defined in these parameters Next, nt because it will select the nt Next the r_t_id because it is a ID for a specific type of my r_t table And last the t_p because it is just a information. I don’t know if it is at all necessary to order it in a specific way when it is a SELECT ALL statement. I should say, that the SC is not the biggest table. I can say how many rows it contains but a estimate could be between <10 and 1000. The next thing to add is, that the SC, in different queries, inserts the data into the SC, and I know that indexes on tables which have insertions can be cost ineffective, but can I somehow create a golden middle way to effective this performance. Don't know if it makes a different but I'm using IBM DB2 version 9.7 database Sincerely Mestika

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• Run multiple MySQL queries based on a series of ifs

  - by OldWest

  I am just getting started on this complex query I need to write and was hoping for any suggestions or feedback regarding table structure and the actual query itself.. I've already created my tables and populated test data, and now just trying to sort out how and what is possible within MySQL. Here is an outline of the problem: End result: Listing of rates based on specific queried criteria (see below): Age: [ 27 ] Spouse Age: [ 25 ] Num of Children: [ 3 ] Zip Code: [ 97128 ] The problem I am running into is each company that provides rates has a unique way of dealing with the rate. And I am looking for the best approach for multiple queries based on the company (one query with results for each company more or less all combined into one result set). Here are some facts: - Each company deals with zip code ranges which assist in the query result. - Each company has a different method of calculating the rate based on the Applicant, Spouse, Num of Children: Example, a) Company A determines rate by: Applicant + Spouse + Child(ren) = rate (age is pertinent to the applicant within a range). b) Company B determines the rate by total number of applicants like: 1, 2, 3, 4, 5, 6+ = rate (and age is ignored). First off, what would I call this type of query? Multiple nested query? And should I intertwine php within it to determine the If()s ... I apologize if this thread lacks sufficient data, so please tell me anything you would like to see.

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• Protocol specification in XML

  - by Mathijs

  Is there a way to specify a packet-based protocol in XML, so (de)serialization can happen automatically? The context is as follows. I have a device that communicates through a serial port. It sends and receives a byte stream consisting of 'packets'. A packet is a collection of elementary data types and (sometimes) other packets. Some elements of packets are conditional; their inclusion depends on earlier elements. I have a C# application that communicates with this device. Naturally, I don't want to work on a byte-level throughout my application; I want to separate the protocol from my application code. Therefore I need to translate the byte stream to structures (classes). Currently I have implemented the protocol in C# by defining a class for each packet. These classes define the order and type of elements for each packet. Making class members conditional is difficult, so protocol information ends up in functions. I imagine XML that looks like this (note that my experience designing XML is limited): <packet> <field name="Author" type="int32" /> <field name="Nickname" type="bytes" size="4"> <condition type="range"> <field>Author</field> <min>3</min> <max>6</min> </condition> </field> </packet> .NET has something called a 'binary serializer', but I don't think that's what I'm looking for. Is there a way to separate protocol and code, even if packets 'include' other packets and have conditional elements?

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