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• Search implementation dilemma: full text vs. plain SQL

  - by Ethan

  I have a MySQL/Rails app that needs search. Here's some info about the data: Users search within their own data only, so searches are narrowed down by user_id to begin with. Each user will have up to about five thousand records (they accumulate over time). I wrote out a typical user's records to a text file. The file size is 2.9 MB. Search has to cover two columns: title and body. title is a varchar(255) column. body is column type text. This will be lightly used. If I average a few searches per second that would be surprising. It's running an a 500 MB CentOS 5 VPS machine. I don't want relevance ranking or any kind of fuzziness. Searches should be for exact strings and reliably return all records containing the string. Simple date order -- newest to oldest. I'm using the InnoDB table type. I'm looking at plain SQL search (through the searchlogic gem) or full text search using Sphinx and the Thinking Sphinx gem. Sphinx is very fast and Thinking Sphinx is cool, but it adds complexity, a daemon to maintain, cron jobs to maintain the index. Can I get away with plain SQL search for a small scale app?

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• Get percentiles of data-set with group by month

  - by Cylindric

  Hello, I have a SQL table with a whole load of records that look like this: | Date | Score | + -----------+-------+ | 01/01/2010 | 4 | | 02/01/2010 | 6 | | 03/01/2010 | 10 | ... | 16/03/2010 | 2 | I'm plotting this on a chart, so I get a nice line across the graph indicating score-over-time. Lovely. Now, what I need to do is include the average score on the chart, so we can see how that changes over time, so I can simply add this to the mix: SELECT YEAR(SCOREDATE) 'Year', MONTH(SCOREDATE) 'Month', MIN(SCORE) MinScore, AVG(SCORE) AverageScore, MAX(SCORE) MaxScore FROM SCORES GROUP BY YEAR(SCOREDATE), MONTH(SCOREDATE) ORDER BY YEAR(SCOREDATE), MONTH(SCOREDATE) That's no problem so far. The problem is, how can I easily calculate the percentiles at each time-period? I'm not sure that's the correct phrase. What I need in total is: A line on the chart for the score (easy) A line on the chart for the average (easy) A line on the chart showing the band that 95% of the scores occupy (stumped) It's the third one that I don't get. I need to calculate the 5% percentile figures, which I can do singly: SELECT MAX(SubQ.SCORE) FROM (SELECT TOP 45 PERCENT SCORE FROM SCORES WHERE YEAR(SCOREDATE) = 2010 AND MONTH(SCOREDATE) = 1 ORDER BY SCORE ASC) AS SubQ SELECT MIN(SubQ.SCORE) FROM (SELECT TOP 45 PERCENT SCORE FROM SCORES WHERE YEAR(SCOREDATE) = 2010 AND MONTH(SCOREDATE) = 1 ORDER BY SCORE DESC) AS SubQ But I can't work out how to get a table of all the months. | Date | Average | 45% | 55% | + -----------+---------+-----+-----+ | 01/01/2010 | 13 | 11 | 15 | | 02/01/2010 | 10 | 8 | 12 | | 03/01/2010 | 5 | 4 | 10 | ... | 16/03/2010 | 7 | 7 | 9 | At the moment I'm going to have to load this lot up into my app, and calculate the figures myself. Or run a larger number of individual queries and collate the results.

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• VB.NET vs. C#.NET?

  - by Onion-Knight

  Hello everyone, The company I work for has all of its legacy ("legacy" being used rather liberally in this context) code in VB.NET. They have about 6000+ lines of VB.NET code, so all of the developers are comfortable with it. We have started to develop a new product, and are finding that some modules are easier to complete in C# than in VB.NET, such as Interprocess Communication via WCF. The things our product will eventually need to do are as follows: Communicate via IPC between Windows Services, Silverlight, and WinForms Handle parallization, and all the complexity that comes along with it Windows Service and WinForms development ASP.NET, AJAX, and Silverlight development Database (SQL) access Lots of event handling (Sync and Async events) My question is: Given the type of work we will be doing to complete our product, are there features of one language that will make life easier that the other does not have? And if so, it is worth asking the developers to switch to a language they are less comfortable with? I was hoping to keep this as objective as possible, by listing exactly what type of work we will be doing with the product. Please don't turn this into a VB/C# holy war. Thanks, Onion-Knight

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• Reduce size and change text color of the bootstrap-datepicker field

  - by Lisarien

  Programing an Android application based on HTML5/JQuery launching in a web view, I'm using the Eternicode's bootstrap-datepicker. BTW I'm using Jquery 1.9.1 and Bootstrap 2.3.2 with bootstrap-responsive. The picker is working fine but unfortunately I get yet two issues which I was not able to solve at this time: the picker theme is not respected and some dates are not readable (see the attached picture). Some there is css conflict such as the datepicker's font is displayed white on white background. I'm not able to reduce the size of the date picker field such as it holds on alone row. My markup code is: <div class="row-fluid" style="margin-right:0px!important"> <label id="dateId" class="span6">One Date</label> <div id="datePurchase" class="input-append date"> <input data-format="yyyy-MM-dd" type="text" /> <span class="add-on"> <i data-time-icon="icon-time" data-date-icon="icon-calendar"></i> </span> </div> </div> I init the datepicker by Javascript: $("#dateId").datetimepicker({ pickTime: false, format: "dd/MM/yyyy", startDate: startDate, endDate: endDate, autoclose: true }); $("#dateId").on("changeDate", onChangeDate); Do you get any idea about these issues? Thanks very much

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• Displaying timecode using NSTimer and NSDateFormatter

  - by Chris B

  Hi. I am very close to completing my first iphone app and it has been a joy. I am trying to add running timecode using the current time via an NSTimer displaying the current time (NSDate) on a UILabel. NSDate is working fine for me, showing hour, minute, second, milliseconds. But instead of milliseconds, I need to show 24 frames per second. The problem is that I need the frames per second to be synced 100% with the hour, minute and second, so I can't add the frames in a separate timer. I tried that and had it working but the frame timer was not running in sync with the date timer. Can anyone help me out with this? Is there a way to customize NSDateFormatter so that I can have a date timer formatted with 24 frames per second? Right now I'm limited to formatting just hours, minutes, seconds, and milliseconds. Here's the code I'm using right now -(void)runTimer { // This starts the timer which fires the displayCount method every 0.01 seconds runTimer = [NSTimer scheduledTimerWithTimeInterval: .01 target: self selector: @selector(displayCount) userInfo: nil repeats: YES]; } //This formats the timer using the current date and sets text on UILabels - (void)displayCount; { NSDateFormatter *formatter = [[[NSDateFormatter alloc] init] autorelease]; NSDate *date = [NSDate date]; // This will produce a time that looks like "12:15:07:75" using 4 separate labels // I could also have this on just one label but for now they are separated // This sets the Hour Label and formats it in hours [formatter setDateFormat:@"HH"]; [timecodeHourLabel setText:[formatter stringFromDate:date]]; // This sets the Minute Label and formats it in minutes [formatter setDateFormat:@"mm"]; [timecodeMinuteLabel setText:[formatter stringFromDate:date]]; // This sets the Second Label and formats it in seconds [formatter setDateFormat:@"ss"]; [timecodeSecondLabel setText:[formatter stringFromDate:date]]; //This sets the Frame Label and formats it in milliseconds //I need this to be 24 frames per second [formatter setDateFormat:@"SS"]; [timecodeFrameLabel setText:[formatter stringFromDate:date]]; }

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• SQL Server Compact timed out waiting for a lock

  - by jankhana

  Hi all, I'm having an application in that i use Sql Compact 3.5 with VS2008. I'm running multiple threads in my application which contacts the compact database and accesses the row. It selects and deletes those rows in a fashion i.e selecting and giving to the application 5 rows and deleting those rows from the table. It works great with a single thread but if i use multiple threads i.e if 3 or more threads are running I get very often the TimeOut Error!!! I have increased the Time out property in the connection string but it didn't give me expected result. The error log is as follow: SQL Server Compact timed out waiting for a lock. The default lock time is 2000ms for devices and 5000ms for desktops. The default lock timeout can be increased in the connection string using the ssce: default lock timeout property. [ Session id = 5,Thread id = 4204,Process id = 4808,Table name = XXX,Conflict type = x lock (s blocks),Resource = TAB ] The Query that I use to retrieve is as follows: " select Top(5) * from TableName order by id; delete from TableName where id in(select top(5) id from TableName order by id); " Is there any way by which we can avoid this Time Out exception??????? The above query I un as a transaction in VS2008 one using SQLCECommand and the other using SqlCEDataAdapter. Any Idea!!!!!! Reply

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• What is the best software design to use in this scenario

  - by domdefelice

  I need to generate HTML snippets using jQuery. The creation of those snippets depends on some data. The data is stored server-side, in session (where PHP is used). At the moment I achieved this - retrieving the data from the server via AJAX in form of JSON - and building the snippets via specific javascript functions that read those data The problem is that the complexity of the data is getting bigger and hence the serialization into JSON is getting even more difficult since I can't do it automatically. I can't do it automatically because some information are sensible so I generate a "stripped" version to send to the client. I know it is difficult to understand without any code to read, but I am hoping this is a common scenario and would be glad for any tip, suggestion or even design-pattern you can give me. Should I store both a complete and a stripped data on the server and then use some library to automatically generate the JSON from the stripped data? But this also means I have to get the two data synchronized. Or maybe I could move the logic server-side, this way avoiding sending the data. But this means sending javascript code (since I rely on jQuery). Maybe not a good idea. Feel free to ask me more details if this is not clear. Thank you for any help

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• Why does autoboxing in Java allow me to have 3 possible values for a boolean?

  - by John

  Reference: http://java.sun.com/j2se/1.5.0/docs/guide/language/autoboxing.html If your program tries to autounbox null, it will throw a NullPointerException. javac will give you a compile-time error if you try to assign null to a boolean. makes sense. assigning null to a Boolean is a-ok though. also makes sense, i guess. but let's think about the fact that you'll get a NPE when trying to autounbox null. what this means is that you can't safely perform boolean operations on Booleans without null-checking or exception handling. same goes for doing math operations on an Integer. for a long time, i was a fan of autoboxing in java1.5+ because I thought it got java closer to be truly object-oriented. but, after running into this problem last night, i gotta say that i think this sucks. the compiler giving me an error when I'm trying to do stuff with an uninitialized primitive is a good thing. I think I may be misunderstanding the point of autoboxing, but at the same time I will never accept that a boolean should be able to have 3 values. can anyone explain this? what am i not getting?

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• how can I speed up insertion of many rows to a table via ADO.NET?

  - by jcollum

  I have a table that has 5 columns: AcctId (int), Address1 (varchar), Address2 (varchar), Person1 (varchar), Person2 (varchar) . I'm generating random data to insert into this table via a C# console application. I've tried doing this random data insert via SQL-Server and decided it was not a good solution -- SQL is not good at random on an each-row basis. Generating the random data -- 975k rows of it -- takes a minimal amount of time. It's in a List of custom objects. I need to take this random data and update many rows in the database with the new random data. I tried updating the rows one at a time, very slow because of the repeated searching of the List object in code. So I think the best approach is to put all the randomized data into a table in the database, then update all the other tables that use this data. I.e. UPDATE t SET t.Address1=d.Address1 FROM Table1 t INNER JOIN RandomizedData d ON d.AcctId = t.Acct_ID. The database is very un-normalized so this Acct data is sprinkled all over the place. I've got no control of the normalization. So, having decided to insert all of the randomized data into a single table, I set out to create insert scripts: USE TheDatabase Insert tmp_RandomizedData SELECT 1,'4392 EIGHTH AVE','','JENNIFER CARTER','BARBARA CARTER' UNION ALL SELECT 2,'2168 MAIN ST','HNGR F','DANIEL HERNANDEZ','SUSAN MARTIN' // etc another 98 times... // FYI, this is not real data! I'm building this INSERT script in batches of 100. It's taking on average 175 ms to run each insert. Does this seem like a long time? It's going to take about 35 mins to run the whole insert. The table doesn't have a primary key or any indexes. I was planning on adding those after all the data in inserted (thinking that that would be faster). Is there a better way to do this?

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• wxpython GUI and multiprocessing - how to send data back from the long running process

  - by wxpydon

  Hello everyone, Trying to run a time consuming task from a wxpython GUI. The basic idea is to start the long time task from the GUI (pressing a button) and then, a static text on the dialog should be updated from it. First I tried some threading (http://wiki.wxpython.org/LongRunningTasks and many other resourses seen), and I want to show back the messages using Publisher.class. It didn't went so well, after a message or two, the GUI seems to frozen. Now I want to achieve that with multiprocessing. I have this method inside my 'GUI' class: def do_update(self, e): self.txt_updatemsg.SetLabel("Don't stop this \n") ... pub = Publisher() # i tried also calling directly from dbob object # Publisher() is a singleton so this must be useless? pub.subscribe(self.__update_txt_message, ('updatedlg', 'message')) dbob = dbutils.DBUtils() # DBUtils is the class with 'long time' tasks dbob.publisher = pub p = Process(target=self.do_update_process, args=(dbob,)) p.start() while p.is_alive: wx.Yield def do_update_process(self, dbob): dbob.do_update() __update_txt_message is a simple function what sets the static text on dialog. Question is: how can I send back some text messages from this Process (just simple text, that's all I need) Thanks guys!

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• Unexpected performance curve from CPython merge sort

  - by vkazanov

  I have implemented a naive merge sorting algorithm in Python. Algorithm and test code is below: import time import random import matplotlib.pyplot as plt import math from collections import deque def sort(unsorted): if len(unsorted) <= 1: return unsorted to_merge = deque(deque([elem]) for elem in unsorted) while len(to_merge) > 1: left = to_merge.popleft() right = to_merge.popleft() to_merge.append(merge(left, right)) return to_merge.pop() def merge(left, right): result = deque() while left or right: if left and right: elem = left.popleft() if left[0] > right[0] else right.popleft() elif not left and right: elem = right.popleft() elif not right and left: elem = left.popleft() result.append(elem) return result LOOP_COUNT = 100 START_N = 1 END_N = 1000 def test(fun, test_data): start = time.clock() for _ in xrange(LOOP_COUNT): fun(test_data) return time.clock() - start def run_test(): timings, elem_nums = [], [] test_data = random.sample(xrange(100000), END_N) for i in xrange(START_N, END_N): loop_test_data = test_data[:i] elapsed = test(sort, loop_test_data) timings.append(elapsed) elem_nums.append(len(loop_test_data)) print "%f s --- %d elems" % (elapsed, len(loop_test_data)) plt.plot(elem_nums, timings) plt.show() run_test() As much as I can see everything is OK and I should get a nice N*logN curve as a result. But the picture differs a bit: Things I've tried to investigate the issue: PyPy. The curve is ok. Disabled the GC using the gc module. Wrong guess. Debug output showed that it doesn't even run until the end of the test. Memory profiling using meliae - nothing special or suspicious. ` I had another implementation (a recursive one using the same merge function), it acts the similar way. The more full test cycles I create - the more "jumps" there are in the curve. So how can this behaviour be explained and - hopefully - fixed? UPD: changed lists to collections.deque UPD2: added the full test code UPD3: I use Python 2.7.1 on a Ubuntu 11.04 OS, using a quad-core 2Hz notebook. I tried to turn of most of all other processes: the number of spikes went down but at least one of them was still there.

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• MongoDB - proper use of collections?

  - by zmg

  In Mongo my understanding is that you can have databases and collections. I'm working on a social-type app that will have blogs and comments (among other things) and had previously be using MySQL and pretty heavy partitioning in an attempt to limit possible concurrency issues. With MySQL I've stuffed all my user data into a _user database with several tables to further partition the data (blogs, pages, etc). My immediate reaction with Mongo would be to create a 'users' database with one collection per user. In this way user 'zach' blog entries would go into the 'zach' collection with associated comments and such becoming sub-objects in the same collection. Basically like dynamically creating one table per user in MySQL, but apparently without the complexity and limitations that might impose. Of course since I haven't really used Mongo before I'm having trouble gauging the (ahem..) quality of this idea and the potential problems it might cause down the road. I'd like user data to be treated a lot like a users directory in a *nix environment where user created/non-shared (mostly) gets put into one place (currently with MySQL that would be the appname_users as mentioned above). Most of the users data will be specific to the users page(s). Some of the user data which is queried across all site users (searchable user profiles) is currently kept in a separate database/table and I expect things like this could be put into a appname_system database and be broken up into collections and/or application specific databases (appname_profiles). Anyway, since the available documentation on this is currently a little thin and my experience is extremely limited I thought I might find a little guidance from someone with a better working understanding of the system. On the plus side I'd really already been attempting to treat MySQL as a schema-less document-store and doing this with Mongo seems much more intuitive/sane/rational so I'm really looking forward to getting started. Thanks, Zach

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• Monitor web sites visited using Internet Explorer, Opera, Chrome, Firefox and Safari in Python

  - by Zachary Brown

  I am working on a project for work and have seemed to run into a small problem. The project is a similar program to Web Nanny, but branded to my client's company. It will have features such as website blocking by URL, keyword and web activity logs. I would also need it to be able to "pause" downloads until an acceptable username and password is entered. I found a script to monitor the URL visited in Internet Explorer (shown below), but it seems to slow the browser down considerably. I have not found any support or ideas onhow to implement this in other browsers. So, my questions are: 1). How to I monitor other browser activity / visited URLs? 2). How do I prevent downloading unless an acceptable username and password is entered? from win32com.client import Dispatch,WithEvents import time,threading,pythoncom,sys stopEvent=threading.Event() class EventSink(object): def OnNavigateComplete2(self,*args): print "complete",args stopEvent.set() def waitUntilReady(ie): if ie.ReadyState!=4: while 1: print "waiting" pythoncom.PumpWaitingMessages() stopEvent.wait(.2) if stopEvent.isSet() or ie.ReadyState==4: stopEvent.clear() break; time.clock() ie=Dispatch('InternetExplorer.Application',EventSink) ev=WithEvents(ie,EventSink) ie.Visible=1 ie.Navigate("http://www.google.com") waitUntilReady(ie) print "location",ie.LocationName ie.Navigate("http://www.aol.com") waitUntilReady(ie) print "location",ie.LocationName print ie.LocationName,time.clock() print ie.ReadyState

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• 1. I fill out a form & click submit. 2. I get the results page. Goal: Get the same results without f

  - by Chris

  This is my first time posting - I greatly appreciate any and all guidance on this subject. Background: I am building a Real Estate web site. I would like to use the free IDX data provided by my local MLS board. The MLS board does not allow me the option of displaying a predefined search and only provides me with a link to the search field. after filling out the search field, I am able to view the results. Goal: I would like to bypass this step and frame the results page into a GoDaddy website I am building, which supports HTML. Here is a link to the search page: http://fgcmls.rapmls.com/scripts/mgrqispi.dll?APPNAME=Fortmyers&PRGNAME=MLSLogin&ARGUMENT=vBSJvLQtMcbg7F0O0KnXDiggv%2F12B0S6Ss9wv4510QA%3D&KeyRid=1 I am trying to only show the listings that appear in my neighborhood. Options include: 1. Property Type - Residential 2. GEO Area - FM11 3. Developments: Fiddlesticks Country Club Once this criteria is entered, I have the page needed to make this project work. Thank all of you for taking the time to read this and for the time you spend helping me out. Best regards, Chris

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• How can I do rapid application development with ASP.NET MVC?

  - by Erik Forbes

  I've been given a short amount of time (~80 hours to start with) to replace an existing Access database with a full-blown SQL + Web system, and I'm enumerating my options. I would like to use ASP.NET MVC, but I'm unsure of how to use it effectively with my short timetable. For the database backend I'll be using Linq to SQL as it's a product I already know and can get something working with it quickly. Does anyone have any experience with using ASP.NET MVC in this way and can share some insight? Edit: The reason I've been interested in ASP.NET MVC is because I know (100% confirmed) that there will be more work to do after this first round, and I'd like my maintenance work to be as easy as possible. In my experience Webforms applications tend to break down over repeated maintenance, despite discipline. Maybe there's a middle ground? How difficult would it to be for me to, say, build the app with Webforms, then migrate it to MVC later when I have more time budgeted to the project? Edit 2: Further background: the Access application I'm replacing is used in some capacity by everyone in the building, and since it was upgraded from Access 98 to 2003 it's been crashing daily, causing hours of lost productivity as people have to re-enter data since the last backup. This is the reason for the short amount of time - this is a critical business function, and they can't afford to keep re-entering data on a daily basis.

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• Invert a string: Recursion vs iteration in javascript

  - by steweb

  Hi all, one month ago I've been interviewed by some google PTO members. One of the questions was: Invert a string recursively in js and explain the running time by big O notation this was my solution: function invert(s){ return (s.length > 1) ? s.charAt(s.length-1)+invert(s.substring(0,s.length-1)) : s; } Pretty simple, I think. And, about the big-o notation, I quickly answered O(n) as the running time depends linearly on the input. - Silence - and then, he asked me, what are the differences in terms of running time if you implement it by iteration? I replied that sometimes the compiler "translate" the recursion into iteration (some programming language course memories) so there are no differences about iteration and recursion in this case. Btw since I had no feedback about this particular question, and the interviewer didn't answer "ok" or "nope", I'd like to know if you maybe agree with me or if you can explain me whether there could be differences about the 2 kind of implementations. Thanks a lot and Regards!

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• How to make UIButton work like Launcher in SpringBoard, when pressed for long timeinterval

  - by KayKay

  In my ViewController I am using UIButton which triggers some action when touchedUpInside. Upto here no problem, but i also want to add another action for touchDown event. More precisely i dont have an idea how to add that action to which event, that will work the same as when App-Icon is pressed longer in springboard which causes springboard enter in editing mode.Actually what i want is : when this button is kept holding for ,say about 2 seconds it will pop-up an alertView without touch being heldUp (with finger is still on button). I have tried with 2 NSdate difference, one of which is allocated when touchedDown and other when touchUpInside. Its working and popping alert,but only after touchedUpInside. I want it to show alert without touch being removed. Here is the code. (IBAction)touchedDown:(id)sender { momentTouchedDown = [[NSDate alloc] init];//class variable NSLog(@"touched down"); } - (IBAction)touchUpInside:(id)sender { NSLog(@"touch lifted Up\n"); NSDate *momentLifted = [[NSDate alloc] init]; double timeInterval = [momentLifted timeIntervalSinceDate:momentTouchedDown]; NSLog(@"time lifted = %@, time down = %@, time diff = %@", momentLifted, momentTouchedDown, [NSString stringWithFormat:@"%g",timeInterval]); [momentLifted release]; if(timeInterval > 2.0) { NSLog(@"AlertBox has been fired"); UIAlertView *alert = [[UIAlertView alloc] initWithTitle:@"Yes" message:@""//msg delegate:self cancelButtonTitle:@"Cancel" otherButtonTitles:@"OK" , nil]; [alert show]; [alert release]; } } Please provide me an insight..thanks for help in advance.

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• iPhone UI layout debugging

  - by Cruinh

  I have this chronic issue with iPhone UI development where views sometimes seem to appear on the screen in a location different than what is reported by their frame property. Here is what I am doing to try to debug the issue: UIView *currentView = self.view; while (currentView!=nil) { NSLog(@"frame: %f,%f,%f,%f", currentView.frame.origin.x, currentView.frame.origin.y, currentView.frame.size.width, currentView.frame.size.height); currentView = currentView.superview; } I expect this should show me the coordinates and size of each element up the hierarchy from the given view to the app's root UIWindow element, with the coordinates for each element relative to its parent. However, that does not seem to be the case. In my current situation, I have a UI I'm trying to debug where every other time I rotate the device, the whole UI shifts up or down 20 pixels, yet the code block above reports exactly the same numbers every time. I tried calling the above code after as much as a second delay, but that the numbers still come out the same each time. Does anyone know a better way to inspect the screen coordinates of UI elements? If I can detect when one is wrong, I can compensate for the problem when it appears.

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• Help needed in grokking password hashes and salts

  - by javafueled

  I've read a number of SO questions on this topic, but grokking the applied practice of storing a salted hash of a password eludes me. Let's start with some ground rules: a password, "foobar12" (we are not discussing the strength of the password). a language, Java 1.6 for this discussion a database, postgreSQL, MySQL, SQL Server, Oracle Several options are available to storing the password, but I want to think about one (1): Store the password hashed with random salt in the DB, one column Found on SO and elsewhere is the automatic fail of plaintext, MD5/SHA1, and dual-columns. The latter have pros and cons MD5/SHA1 is simple. MessageDigest in Java provides MD5, SHA1 (through SHA512 in modern implementations, certainly 1.6). Additionally, most RDBMSs listed provide methods for MD5 encryption functions on inserts, updates, etc. The problems become evident once one groks "rainbow tables" and MD5 collisions (and I've grokked these concepts). Dual-column solutions rest on the idea that the salt does not need to be secret (grok it). However, a second column introduces a complexity that might not be a luxury if you have a legacy system with one (1) column for the password and the cost of updating the table and the code could be too high. But it is storing the password hashed with a random salt in single DB column that I need to understand better, with practical application. I like this solution for a couple of reasons: a salt is expected and considers legacy boundaries. Here's where I get lost: if the salt is random and hashed with the password, how can the system ever match the password? I have theory on this, and as I type I might be grokking the concept: Given a random salt of 128 bytes and a password of 8 bytes ('foobar12'), it could be programmatically possible to remove the part of the hash that was the salt, by hashing a random 128 byte salt and getting the substring of the original hash that is the hashed password. Then re hashing to match using the hash algorithm...??? So... any takers on helping. :) Am I close?

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• Linear feedback shift register?

  - by Mattia Gobbi

  Lately I bumped repeatedly into the concept of LFSR, that I find quite interesting because of its links with different fields and also fascinating in itself. It took me some effort to understand, the final help was this really good page, much better than the (at first) cryptic wikipedia entry. So I wanted to write some small code for a program that worked like a LFSR. To be more precise, that somehow showed how a LFSR works. Here's the cleanest thing I could come up with after some lenghtier attempts (Python): def lfsr(seed, taps): sr, xor = seed, 0 while 1: for t in taps: xor += int(sr[t-1]) if xor%2 == 0.0: xor = 0 else: xor = 1 print xor sr, xor = str(xor) + sr[:-1], 0 print sr if sr == seed: break lfsr('11001001', (8,7,6,1)) #example I named "xor" the output of the XOR function, not very correct. However, this is just meant to show how it circles through its possible states, in fact you noticed the register is represented by a string. Not much logical coherence. This can be easily turned into a nice toy you can watch for hours (at least I could :-) def lfsr(seed, taps): import time sr, xor = seed, 0 while 1: for t in taps: xor += int(sr[t-1]) if xor%2 == 0.0: xor = 0 else: xor = 1 print xor print time.sleep(0.75) sr, xor = str(xor) + sr[:-1], 0 print sr print time.sleep(0.75) Then it struck me, what use is this in writing software? I heard it can generate random numbers; is it true? how? So, it would be nice if someone could: explain how to use such a device in software development come up with some code, to support the point above or just like mine to show different ways to do it, in any language Also, as theres not much didactic stuff around about this piece of logic and digital circuitry, it would be nice if this could be a place for noobies (like me) to get a better understanding of this thing, or better, to understand what it is and how it can be useful when writing software. Should have made it a community wiki? That said, if someone feels like golfing... you're welcome.

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• Rails : fighting long http response times with ajax. Is it a good idea? Please, help with implementa

  - by baranov

  Hi, everybody! I've googled some tutorials, browsed some SO answers, and was unable to find a recipe for my problem. I'm writing a web site which is supposed to display almost realtime stock chart. Data is stored in constantly updating MySQL database, I wrote a find_by_sql query code which fetches all the data I need to get my chart drawn. Everything is ok, except performance - it takes from one second to one minute for different queries to fetch all the data from the database, this time includes necessary (My)SQL-server side calculations. This is simply unacceptable. I got the following idea: if the data is queried from the MySQL server one point a time instead of entire dataset, it takes only about 1-100ms to get an individual point. I imagine the data fetch process might be browser-driven. After the user presses the button in order to get a chart drawn, controller makes one request to the database and renders, say, a progress bar, say 1% ready. When the browser gets the response, it immediately makes an (ajax) request, and the server fetches the next piece of data and renders "2%". And so on, until all the data is ready and the server displays the requested chart. Could this be implemented in rails+js, is there a tutorial for solving a similar problem on the Web? I suppose if the thing is feasible at all, somebody should have already done this before. I have read several articles about ajax, I believe I do understand general principles, but never did nontrivial ajax programming myself. Thanks for your time!

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• Get information form WebPage.

  - by william-hu

  I want to set up an app which can get the information from a particular web page. Then i display the value which got from that page to the iPhone user. Detail:In the webpage on server ,there is the schedule for bus time. If the user input origin and terminus then show the user the time information(list on webpage) in a label. That's all. What i have finished is : Open the iphone app, input two value(origin and terminus) to UITextField. Send the URL to server. Get the page, and show in UIWebView. What my problem next is how should i get the information form that page into another two labels to give the user about the bus time. I have store data in my Array receiveData: self.receivedData = data; I am not clear the data i received is XML or what? And how should i pick-up the value i want. (should i save the value to property list and the read the value?) Thank you so much!

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• Executing sequential stored procedures; works in query analyzer, doesn't in my .NET application

  - by evanmortland

  Hello, I have an audit record table that I am writing to. I am connecting to MyDb, which has a stored procedure called 'CreateAudit', which is a passthrough stored procedure to another database on the same machine called MyOther DB with a stored procedure called 'CreatedAudit' as well. In other words in MyDB I have CreateAudit, which does the following EXEC dbo.MyOtherDB.CreateAudit. I call the MyDb CreateAudit stored procedure from my application, using subsonic as the DAL. The first time I call it, I call it with the following (pseudocode): Result = CreateAudit(recordId, "Opened") One line after that, I call: Result2 = CreateAudit(recordId, "Closed") In my second stored procedure it is supposed to mark the record that was created by the CreateAudit(recordId, "Opened") with a status of closed. It works great if I run them independently of one another, but when they run in sequence in the application, the record is not marked as "Closed". When I run SQL profiler I see that both queries ran, and if I copy the queries out and run them from query analyzer the record gets marked as closed 100% of the time! When I run it from the application, about once every 20 times or so, the record is successfully marked closed - the other 19 times nothing happens, but I do not get an error! Is it possible for the .NET app to skip over the ouput from the first stored procedure and start executing the second stored procedure before the record in the first is created? When I add a "WAITFOR DELAY '00:00:00:003'" to the top of my stored procedure, the record is also closed 100% of the time. My head is spinning, any ideas why this is happening! Thanks for any responses, very interested in hearing how this can happen.

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• How to find the latest row for each group of data

  - by Jason

  Hi All, I have a tricky problem that I'm trying to find the most effective method to solve. Here's a simplified version of my View structure. Table: Audits AuditID | PublicationID | AuditEndDate | AuditStartDate 1 | 3 | 13/05/2010 | 01/01/2010 2 | 1 | 31/12/2009 | 01/10/2009 3 | 3 | 31/03/2010 | 01/01/2010 4 | 3 | 31/12/2009 | 01/10/2009 5 | 2 | 31/03/2010 | 01/01/2010 6 | 2 | 31/12/2009 | 01/10/2009 7 | 1 | 30/09/2009 | 01/01/2009 There's 3 query's that I need from this. I need to one to get all the data. The next to get only the history data (that is, everything but exclude the latest data item by AuditEndDate) and then the last query is to obtain the latest data item (by AuditEndDate). There's an added layer of complexity that I have a date restriction (This is on a per user/group basis) where certain user groups can only see between certain dates. You'll notice this in the where clause as AuditEndDate<=blah and AuditStartDate=blah Foreach publication, select all the data available. select * from Audits Where auditEndDate<='31/03/10' and AuditStartDate='06/06/2009'; foreach publication, select all the data but Exclude the latest data available (by AuditEndDate) select * from Audits left join (select AuditId as aid, publicationID as pid and max(auditEndDate) as pend from Audit where auditenddate <= '31/03/2009' /* user restrict / group by pid) Ax on Ax.pid=Audit.pubid where pend!=Audits.auditenddate AND auditEndDate<='31/03/10' and AuditStartDate='06/06/2009' / user restrict */ Foreach publication, select only the latest data available (by AuditEndDate) select * from Audits left join (select AuditId as aid, publicationID as pid and max(auditEndDate) as pend from Audit where auditenddate <= '31/03/2009'/* user restrict / group by pid) Ax on Ax.pid=Audit.pubid where pend=Audits.auditenddate AND auditEndDate<='31/03/10' and AuditStartDate='06/06/2009' / user restrict */ So at the moment, query 1 and 3 work fine, but query 2 just returns all the data instead of the restriction. Can anyone help me? Thanks jason

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• How to react when asked a question you already know during an interview

  - by DevNull

  The short story:- If you are asked a tough algorithmic/puzzle question during an interview, whose solution is already known to you, do you:- Honestly tell the interviewer that you know this question already? -- this could result in bursting the interviewer's ego and him increasing the complexity level of the subsequent questions. Do an Oscar deserving performance and act as if you are thinking and trying hard and slowly getting to the solution? -- depending on your acting skills, could majorly impress the interviewer making the rest of the interview easier. Long story:- OK, this question comes as a result of what happened to me in a recent telephonic interview that I gave - the interview was supposed to be all algorithmic. The interviewer started with an algorithmic question which I had luckily already seen here on Stackoverflow. The best solution to that problem is not very intuitive and is more of a you-get-it-if-you-know-it kind. Now, just to not disappoint the interviewer too much, I took a few seconds as if I was pondering on the problem and then blurted out the answer which I knew too well having read and admired it on SO already. But I guess that gave it away to the interviewer that I already knew this question and since then, he started asking me for more efficient solutions and I kept coming up with approaches (even if not correct or more efficient, but I did touch a lot of different data structures and algos) and he kept asking for more efficient solutions and generally seemed put off by my initial salvo which was unexpected. What should I have done? Cheers!

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