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R and version control for the solo data analyst

- by Jeromy Anglim

Many data analysts that I respect use version control. For example: http://github.com/hadley/ See comments on http://permut.wordpress.com/2010/04/21/revision-control-statistics-bleg/ However, I'm evaluating whether adopting a version control system such as git would be worthwhile. A brief overview: I'm a social scientist who uses R to analyse data for research publications. I don't currently produce R packages. My R code for a project typically includes a few thousand lines of code for data input, cleaning, manipulation, analyses, and output generation. Publications are typically written using LaTeX. With regards to version control there are many benefits which I have read about, yet they seem to be less relevant to the solo data analyst. Backup: I have a backup system already in place. Forking and rewinding: I've never felt the need to do this, but I can see how it could be useful (e.g., you are preparing multiple journal articles based on the same dataset; you are preparing a report that is updated monthly, etc) Collaboration: Most of the time I am analysing data myself, thus, I woudln't get the collaboration benefits of version control. There are also several potential costs involved with adopting version control: Time to evaluate and learn a version control system A possible increase in complexity over my current file management system However, I still have the feeling that I'm missing something. General guides on version control seem to be addressed more towards computer scientists than data analysts. Thus, specifically in relation to data analysts in circumstances similar to those listed above: Is version control worth the effort? What are the main pros and cons of adopting version control? What is a good strategy for getting started with version control for data analysis with R (e.g., examples, workflow ideas, software, links to guides)?

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Deserializing a complex JSON result (array of dictionaries) with TouchJSON

- by jpm

I did a few tests with TouchJSON last night and it worked pretty well in general for simple cases. I'm using the following code to read some JSON content from a file, and deserialize it: NSString *jsonString = [[NSString alloc] initWithContentsOfFile:@"data.json"]; NSData *jsonData = [jsonString dataUsingEncoding:NSUTF32BigEndianStringEncoding]; NSError *error = nil; NSDictionary *items = [[CJSONDeserializer deserializer] deserializeAsDictionary:jsonData error:&error]; NSLog(@"total items: %d", [items count]); NSLog(@"error: %@", [error localizedDescription]); That works fine if I have a very simple JSON object in the file (i.e. a dictionary): {"id": "54354", "name": "boohoo"} This way I was able to get access to the array of values, as I wanted to get the item based on its index within the list: NSArray *items_list = [items allValues]; NSString *name = [items_list objectAtIndex:1]; (I understand that I could have fetched the name with the dictionary API) Now I would like to deserialize a semi-complex JSON string, which represents an array of dictionaries. An example of such a JSON string is below: [{"id": "123456", "name": "touchjson"}, {"id": "3456", "name": "bleh"}] When I try to run the same code above against this new content in the data.json file, I don't get any results back. My NSLog() call says "total items: 0", and no error is coming back in the NSError object. Any clues on what is going on? I'm completely lost on what to do, as there isn't much documentation available for TouchJSON, and much less usage examples.

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Orca: extracting files from merge module

- by Mystagogue

All I want is a command-line tool that can extract files from a merge module (.msm) onto disk. I looked up Orca (version 3.1), whose documentation states: Many merge module options can be specified from the command line... Extracting Files from a Merge Module Orca supports three different methods for extracting files contained in a merge module. Orca can extract the individual CAB file, extract the files into a module tree and extract the files into a source image once it has been merged into a target database... Extracting Files To extract the individual files from a merge module, use the ... -x ... option on the command line, where is the desired path to the new directory tree. The specified path is used as the root path for the extracted files. All files are extracted from the CAB file embedded in the module and placed in the specified path. The directory layout for the extracted files is based on the directory tree of the merge module. It mostly sounds like exactly what I need. But when I try it, orca simply opens up an editor (with info on the msm I specified) and then does nothing. I've tried a variety of command lines: orca -x theDirectory theModule.msm orca theModule.msm -x theDirectory ...and others. I get nowhere. The closest I've gotten was this: orca -q -x theDirectory -m theModule.msm ...but then it complains that I didn't specifiy a database to merge into. But I'm not trying to merge anything, no less into a database. I just want the files extracted. Can someone explain what I'm doing wrong with the command line options?

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WPF TreeViewItem Context Menu Unhighlights Item

- by Snea

I have been having problems with this for some time now, and have come up with some less-than-desirable solutions. The problem is that when a TreeViewItem's context menu is opened, the TreeViewItem is greyed out. Is it possible for a TreeViewItem to stay highlighted while its ContextMenu is open? The problem with the TreeViewItem greying out, is that it gives no relation to the context menu and the TreeViewItem, and it looks ugly. Generally, the code I use for setting a context menu is this. Sometimes the context menu will be generated by the code with a PreviewRightMouseButtonDown EventSetter, but it doesn't make a difference. <TreeView> <TreeView.Resources> <Style TargetType="{x:Type TreeViewItem}"> <Setter Property="ContextMenu"> <Setter.Value> <ContextMenu> <MenuItem Header="Menu Item 1" /> <MenuItem Header="Menu Item 2" /> </ContextMenu> </Setter.Value> </Setter> </Style> </TreeView.Resources> <TreeViewItem Header="Item 1"> <TreeViewItem Header="Sub-Item 1"/> </TreeViewItem> <TreeViewItem Header="Item 2"></TreeViewItem> </TreeView> So far the only solution I have found is to override the "grey" unfocused color with the focused color, but then the TreeView never seems unfocused, such as when another control is clicked on. I have had problems with ListViews as well.

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Using PHP substr() and strip_tags() while retaining formatting and without breaking HTML

- by Peter

I have various HTML strings to cut to 100 characters (of the stripped content, not the original) without stripping tags and without breaking HTML. Original HTML string (288 characters): $content = "<div>With a <span class='spanClass'>span over here</span> and a <div class='divClass'>nested div over <div class='nestedDivClass'>there</div> </div> and a lot of other nested <strong><em>texts</em> and tags in the air <span>everywhere</span>, it's a HTML taggy kind of day.</strong></div>"; When trimming to 100 characters HTML breaks and stripped content comes to about 40 characters: $content = substr($content, 0, 100)."..."; /* output: <div>With a <span class='spanClass'>span over here</span> and a <div class='divClass'>nested div ove... */ Stripping HTML gives the correct character count but obviously looses formatting: $content = substr(strip_tags($content)), 0, 100)."..."; /* output: With a span over here and a nested div over there and a lot of other nested texts and tags in the ai... */ Challenge: To output the character count of strip_tags while retaining HTML formatting and on closing the string finish any started tags: /* <div>With a <span class='spanClass'>span over here</span> and a <div class='divClass'>nested div over <div class='nestedDivClass'>there</div> </div> and a lot of other nested <strong><em>texts</em> and tags in the ai</strong></div>..."; Similar question (less strict on solution provided so far)

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Sample uniformly at random from an n-dimensional unit simplex.

- by dreeves

Sampling uniformly at random from an n-dimensional unit simplex is the fancy way to say that you want n random numbers such that they are all non-negative, they sum to one, and every possible vector of n non-negative numbers that sum to one are equally likely. In the n=2 case you want to sample uniformly from the segment of the line x+y=1 (ie, y=1-x) that is in the positive quadrant. In the n=3 case you're sampling from the triangle-shaped part of the plane x+y+z=1 that is in the positive octant of R3: (Image from http://en.wikipedia.org/wiki/Simplex.) Note that picking n uniform random numbers and then normalizing them so they sum to one does not work. You end up with a bias towards less extreme numbers. Similarly, picking n-1 uniform random numbers and then taking the nth to be one minus the sum of them also introduces bias. Wikipedia gives two algorithms to do this correctly: http://en.wikipedia.org/wiki/Simplex#Random_sampling (Though the second one currently claims to only be correct in practice, not in theory. I'm hoping to clean that up or clarify it when I understand this better. I initially stuck in a "WARNING: such-and-such paper claims the following is wrong" on that Wikipedia page and someone else turned it into the "works only in practice" caveat.) Finally, the question: What do you consider the best implementation of simplex sampling in Mathematica (preferably with empirical confirmation that it's correct)? Related questions http://stackoverflow.com/questions/2171074/generating-a-probability-distribution http://stackoverflow.com/questions/3007975/java-random-percentages

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Pagination in Tab Content of Jquery UI

- by DR.GEWA

I am making a page with Jquery UI TABS. In one of tabs I want to make pagination for comments. I want such thing. When user clicks on the number of the page, the data of the page , which is linked will load via ajax in the tab. Here is my code <script type="text/javascript"> $(function() { $("#tabs").tabs(); }); $('#demo').tabs({ load: function(event, ui) { $('a', ui.panel).click(function() { $(ui.panel).load(this.href); return false; }); } }); </script> How can I change this , so that any link inside the content with lets say with id "pagination" <a href="/coments?page=12&user_id=12" id="pagination">12</a> ?? Thanks beforehand I tried recently like this even and no luck. This is from http://www.bannerite.com/jquerytest/index2.php Here it work <script type="text/javascript"> $(function() { $("#tabs").tabs(); var hijax = function(panel){ $('a', panel).click(function() { /**makes children 'a' on panel load via ajax, hence hijax*/ $(panel).load(this.href, null, function(){ /**recursively apply the hijax to newly loaded panels*/ hijax(panel); }); /**prevents propagation of click to document*/ return false; }); $('form', panel).css({background: 'yellow'}).ajaxForm({ target: panel, }); }; $('#demo ul').tabs({ /**initialize the tabs hijax pattern*/ load: function(tab, panel) { hijax(panel); } }); }); </script> HEre are the HTML part as Karl gived , but no succes. When clicking on Test link its going to another page........ When clicking on I wanted to post HTML here but because of users with less reputation <10 cant give HTML with links I have posted it here http://gevork.ru/2009/12/31/jquery-ui-tab-and-pagination-html/#more-58

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Question on Scala Closure (From "Programming in Scala")

- by Ekkmanz

I don't understand why authors said that Code Listing 9.1 from "Programming in Scala" use closure. In chapter 9, they show how to refactor code into more less duplicated form, from this original code: object FileMatcher { private def filesHere = (new java.io.File(".")).listFiles def filesEnding(query: String) = for (file <- filesHere; if file.getName.endsWith(query)) yield file def filesContaining(query: String) = for (file <- filesHere; if file.getName.contains(query)) yield file def filesRegex(query: String) = for (file <- filesHere; if file.getName.matches(query)) yield file } To the second version: object FileMatcher { private def filesHere = (new java.io.File(".")).listFiles def filesMatching(query: String, matcher: (String, String) => Boolean) = { for (file <- filesHere; if matcher(file.getName, query)) yield file } def filesEnding(query: String) = filesMatching(query, _.endsWith(_)) def filesContaining(query: String) = filesMatching(query, _.contains(_)) def filesRegex(query: String) = filesMatching(query, _.matches(_)) } Which they said that there is no use of closure here. Now I understand until this point. However they introduced the use of closure to refactor even some more, shown in Listing 9.1: object FileMatcher { private def filesHere = (new java.io.File(".")).listFiles private def filesMatching(matcher: String => Boolean) = for (file <- filesHere; if matcher(file.getName)) yield file def filesEnding(query: String) = filesMatching(_.endsWith(query)) def filesContaining(query: String) = filesMatching(_.contains(query)) def filesRegex(query: String) = filesMatching(_.matches(query)) } Now they said that query is a free variable but I don't really understand why they said so? Since ""query"" seems to be passed from top method down to string matching function explicitly.

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Android app resets on orientation change, best way to handle?

- by Anthony Westover

So I am making a basic chess app to play around with some various elements of android programming and so far I am learning a lot, but this time I am lost. When the orientation of the emulator changes the activity gets reset. Based on my research the same thing will happen anytime the application is paused/interrupted, ie. keyboard change, phone call, hitting the home key etc. Obviously, it is not viable to have a chess game constantly reset, so once again I find myself needing to learn how to fix this problem. My research brings up a few main things, overriding the onPaused method in my Activity, listening for Orientation, Keyboard changes in my manifest (via android:configChanges), using Parcelables, or Serialization. I have looked up a lot of sample code using Pacelables, but to be honest it is too confusing. Maybe coming back tomorrow with fresh eyes will be beneficial, but right now the more I look at Parcelables the less sense it makes. My application utilizes a Board object, which has 64 Cell Objects(in an 8x8 2D array), and each cell has a Piece Object, either an actual piece or null if the space is empty. Assuming that I use either Parcelable or Serialization I am assuming that I would have to Parcelize or Serialize each class, Board, Cell, and Piece. First and foremost, is Parcelable or Serialization even the right thing to be looking at for this problem? If so is either Parcelable or Serializable preferred for this? And am I correct in assuming that each of the three objects would have to be Parceled/Serialized? Finally, does anybody have a link to a simple to understand Parcelable tutorial? Anything to help me understand, and stop further headaches down the road when my application expands even further. Any help would be appreciated.

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cookieless sessions with ajax

- by thezver

ok, i know you get sick from this subject. me too :( I've been developing a quite "big application" with PHP & kohana framework past 2 years, somewhat-successfully using my framework's authentication mechanism. but within this time, and as the app grown, many concerning state-preservation issues arisen. main problems are that cookie-driven sessions: can't be used for web-service access ( at least it's really not nice to do so.. ) in many cases problematic with mobile access don't allow multiple simultaneous apps on same browser ( can be resolved by hard trickery, but still.. ) requires many configurations and mess to work 100% right, and that's without the --browser issues ( disabled cookies, old browsers bugs & vulnerabilities etc ) many other session flaws stated in this old thread : http://lists.nyphp.org/pipermail/talk/2006-December/020358.html After a really long research, and without any good library/on-hand-solution to feet my needs, i came up with a custom solution to majority of those problems . Basically, i'ts about emulating sessions with ajax calls, with additional security/performance measures: state preserved by interchanging SID(+hash) with client on ajax calls. state data saved in memcache(or equivalent), indexed by SID security achieved by: appending unpredictible hash to SID egenerating hash on each request & validating it validating fingerprint of client on each request ( referrer,os,browser etc) (*)condition: ajax calls are not simultaneous, to prevent race-condition with session token. (hopefully Ext-Direct solves that for me) From the first glance that supposed to be not-less-secure than equivalent cookie-driven implementation, and at the same time it's simple, maintainable, and resolves all the cookies flaws.. But i'm really concerned because i often hear the rule "don't try to implement custom security solutions". I will really appreciate any serious feedback about my method, and any alternatives. also, any tip about how to preserve state on page-refresh without cookies would be great :) but thats small technical prob. Sorry if i overlooked some similar post.. there are billions of them about sessions . Big thanks in advance ( and for reading until here ! ).

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iPhone: how do i redraw subviews while pinch zooming a uiscrollview

- by Mike

I am developing an iPhone app that places multiple custom UIViews as subviews in a UIScrollView. The subviews are placed on top of each other as transparent views as each view has its own drawing routines that traces parts of the base view. The base view is a UIImageView that is typically a large image that I want the user to be able to pan and zoom in and out of. The problem I am having is that when I zoom in and out of my UIScrollView, the subviews do not redraw themselves while the user is zooming. I can reposition and scale the subviews properly once the zoom is completed, but the user experience is less than desirable. I have not been able to find a way to either hide or redraw the subviews as the zoom is taking place to scale the subviews along with the ImageView. Any ideas? thanks! Here is the code that I have implemented: - (void)scrollViewDidEndZooming:(UIScrollView *)scrollView withView:(UIView *)view atScale:(float)scale { for (UIView *view in subViews) { [view updateView:scale]; } } - (UIView *)viewForZoomingInScrollView:(UIScrollView *) scrollView { return imageView; }

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Improving long-polling Ajax performance

- by Bears will eat you

I'm writing a webapp (Firefox-compatible only) which uses long polling (via jQuery's ajax abilities) to send more-or-less constant updates from the server to the client. I'm concerned about the effects of leaving this running for long periods of time, say, all day or overnight. The basic code skeleton is this: function processResults(xml) { // do stuff with the xml from the server } function fetch() { setTimeout(function () { $.ajax({ type: 'GET', url: 'foo/bar/baz', dataType: 'xml', success: function (xml) { processResults(xml); fetch(); }, error: function (xhr, type, exception) { if (xhr.status === 0) { console.log('XMLHttpRequest cancelled'); } else { console.debug(xhr); fetch(); } } }); }, 500); } (The half-second "sleep" is so that the client doesn't hammer the server if the updates are coming back to the client quickly - which they usually are.) After leaving this running overnight, it tends to make Firefox crawl. I'd been thinking that this could be partially caused by a large stack depth since I've basically written an infinitely recursive function. However, if I use Firebug and throw a breakpoint into fetch, it looks like this is not the case. The stack that Firebug shows me is only about 4 or 5 frames deep, even after an hour. One of the solutions I'm considering is changing my recursive function to an iterative one, but I can't figure out how I would insert the delay in between Ajax requests without spinning. I've looked at the JS 1.7 "yield" keyword but I can't quite wrap my head around it, to figure out if it's what I need here. Is the best solution just to do a hard refresh on the page periodically, say, once every hour? Is there a better/leaner long-polling design pattern that won't put a hurt on the browser even after running for 8 or 12 hours? Or should I just skip the long polling altogether and use a different "constant update" pattern since I usually know how frequently the server will have a response for me?

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Determining the maximum stack depth

- by Joa Ebert

Imagine I have a stack-based toy language that comes with the operations Push, Pop, Jump and If. I have a program and its input is the toy language. For instance I get the sequence Push 1 Push 1 Pop Pop In that case the maximum stack would be 2. A more complicated example would use branches. Push 1 Push true If .success Pop Jump .continue .success: Push 1 Push 1 Pop Pop Pop .continue: In this case the maximum stack would be 3. However it is not possible to get the maximum stack by walking top to bottom as shown in this case since it would result in a stack-underflow error actually. CFGs to the rescue you can build a graph and walk every possible path of the basic blocks you have. However since the number of paths can grow quickly for n vertices you get (n-1)! possible paths. My current approach is to simplify the graph as much as possible and to have less possible paths. This works but I would consider it ugly. Is there a better (read: faster) way to attack this problem? I am fine if the algorithm produces a stack depth that is not optimal. If the correct stack size is m then my only constraint is that the result n is n = m. Is there maybe a greedy algorithm available that would produce a good result here?

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Development Environment in a VM against an isolated development/test network

- by bart

I currently work in an organization that forces all software development to be done inside a VM. This is for a variety of risk/governance/security/compliance reasons. The standard setup is something like: VMWare image given to devs with tools installed VM is customized to suit project/stream needs VM sits in a network & domain that is isolated from the live/production network SCM connectivity is only possible through dev/test network Email and office tools need to be on live network so this means having two separate desktops going at once Heavyweight dev tools in use on VMs so they are very resource hungry Some problems that people complain about are: Development environment runs slower than normal (host OS is windows XP so memory is limited) Switching between DEV machine and Email/Office machine is a pain, simple things like cut and paste are made harder. This is less efficient from a usability perspective. Mouse in particular doesn't seem to work properly using VMWare player or RDP. Need a separate login to Dev/Test network/domain Has anyone seen or worked in other (hopefully better) setups to this that have similar constraints (as mentioned at the top)? In particular are there viable options that would remove the need for running stuff in a VM altogether?

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SQLite NHibernate configuration with .Net 4.0 and vs 2010

- by Berryl

I am having way too much trouble getting my environment straight after switching to 2010 and .net 4.0, so I'd like to break the whole process down once and for all. 1) Which SQLite dll?? I think it is SQLite-1.0.65.1-vs2010rc-net4-setup.zip. Yes? 2) I ran the installer so the dll is in the GAC but I usually find there are less problems if I can just reference the dll stand alone. Is there any reason it needs to be in the GAC, and if not, what's the best way to uninstall it from the GAC (I can get to the GAC folder but it says I need permission to delete the files; should I leave the SQLite Designer dll's there?)? 3) x64. There is an x64 dll in the download. I had problems with SQLite in the past though that I could only resolve by compiling to x86. Can I safely reference the x64 dll and compile to Any CPU now? 4) what is the right NHib config? I have been using the one below, but since the error I get says "Could not create the driver from NHibernate.Driver.SQLite20Driver." that configuration is guilty until proven innocent too? 5) could FNH be a problem too? I don't use the pre-configured fluent SQLite method but FNH has to provide a reference to it for that to work, no? TIA & Cheers, Berryl <hibernate-configuration xmlns="urn:nhibernate-configuration-2.2"> ... <property name="dialect">NHibernate.Dialect.SQLiteDialect</property> <property name="connection.driver_class">NHibernate.Driver.SQLite20Driver</property> <property name="connection.connection_string">Data Source=:memory:;Version=3;New=True;</property> .... </hibernate-configuration>

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Workflow for academic research projects, one-step builds, and the Joel Test

- by Steve

Working alone on academic research sometimes breeds bad habits. With no one else reading my code, I would write a lot of throw-away code, and I would lose track of intermediate results which, weeks or months later, I wish I had retained. My recent attempts to make my personal workflow conform to the Joel Test raised interesting questions. Academic research has inherently different goals than industrial software development, and therefore some aspects of the Joel Test become less valid. Nevertheless, I find these steps to be still valuable for academic research: Do you use source control? Can you make a build in one step? Do you have an up-to-date schedule? Do you have a spec? Of particular use is the one-step build. I find myself more organized now that I have implemented the following "one-step build": In other words, I have a single script, build.py, that accepts Python code, data, and TeX as inputs. The outputs are results, figures, and a paper with all the results filled in. (Yes, I know "build" is probably not accurate in this context, but you get the idea.) By consolidating many small steps into one, I am not backtracking as much as I used to. ...but I'm sure there is still room for improvement. Question: For research projects, which steps of the Joel Test do you still value? Do you have a one-step build? If so, what does yours consist of, i.e., what inputs does it accept, and what output does it generate?

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Correct way to import Blueprint's ie.css via DotLess in a Spark view

- by Chris F

I am using the Spark View Engine for ASP.NET MVC2 and trying to use Blueprint CSS. The quick guide to Blueprint says to add links to the css files like so: <link rel="stylesheet" href="blueprint/screen.css" type="text/css" media="screen, projection"> <link rel="stylesheet" href="blueprint/print.css" type="text/css" media="print">  But I'm using DotLess and wish to simplify Blueprint as suggested here. So I'm doing this in my site.less (which gets compiled to site.min.css by Chirpy): @import "screen.css"; #header { #title { .span-10; .column; } } ... Now my site can just reference site.min.css and it includes blueprint's screen.css, which includes my reset. I can also tack on an @import "print.css" after my @import "screen.css" if desired. But now, I'm trying to figure out the best way to bring in the ie.css file to have Blueprint render correctly in IE6 & IE7. In my Spark setup, I have a partial called _Styles.spark that is brought into the Application.spark and is passed a view model that includes the filenames for all stylesheets to include (and an HtmlExtension to get the full path) and they're added using an "each" iterator. <link each="var styleSheet in Model.Styles" href="${Html.Stylesheet(styleSheet)}" rel="stylesheet" type="text/css" media="all"/> Should I simply put this below the above line in my _Styles.spark file?  Will Spark even process it because it's surrounded by a comment?

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mongodb: insert if not exists

- by LeMiz

Hello, Every day, I receive a stock of documents (an update). What I want to do is inserting each of them if it does not exists. I also want to keep track of the first time I inserted them, and the last time I saw them in an update. I don't want to have duplicate documents. I don't want to remove a document which has previously been saved, but is not in my update. 95% (estimated) of the records are unmodified from day to day. I am using the python driver (pymongo), for that matter. What I currently do is (pseudo-code): for each document in update: existing_document = collection.find_one(document) if not existing_document: document['insertion_date'] = now else: document = existing_document document['last_update_date'] = now my_collection.save(document) My problem is that it is very slow (40 mins for less than 100 000 records, and I have millions of them in the update). I am pretty sure there is something builtin for doing this, but the document for update() is mmmhhh.... a bit terse.... ( http://www.mongodb.org/display/DOCS/Updating ) Can someone give an advice on doing it faster ?

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Simple iPhone drawing app with Quartz 2D

- by Mr guy 4

I am making a simple iPhone drawing program as a personal side-project. I capture touches event in a subclassed UIView and render the actual stuff to a seperate CGLayer. After each render, I call [self setNeedsLayout] and in the drawRect: method I draw the CGLayer to the screen context. This all works great and performs decently for drawing rectangles. However, I just want a simple "freehand" mode like a lot of other iPhone applications have. The way I thought to do this was to create a CGMutablePath, and simply: CGMutablePathRef path; -(void)touchBegan { path = CGMutablePathCreate(); } -(void)touchMoved { CGPathMoveToPoint(path,NULL,x,y); CGPathAddLineToPoint(path,NULL,x,y); } -(void)drawRect:(CGContextRef)context { CGContextBeginPath(context); CGContextAddPath(context,path); CGContextStrokePath(context); } However, after drawing for more than 1 second, performance degrades miserably. I would just draw each line into the off-screen CGLayer, if it were not for variable opacity! The less-than-100% opacity causes dots to be left on the screen connecting the lines. I have looked at CGContextSetBlendingMode() but alas I cannot find an answer. Can anyone point me in the right direction? Other iPhone apps are able to do this with very good efficiency.

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Metaprogramming - self explanatory code - tutorials, articles, books

- by elena

Hello everybody, I am looking into improving my programming skils (actually I try to do my best to suck less each year, as our Jeff Atwood put it), so I was thinking into reading stuff about metaprogramming and self explanatory code. I am looking for something like an idiot's guide to this (free books for download, online resources). Also I want more than your average wiki page and also something language agnostic or preferably with Java examples. Do you know of such resources that will allow to efficiently put all of it into practice (I know experience has a lot to say in all of this but i kind of want to build experience avoiding the flow bad decisions - experience - good decisions)? EDIT: Something of the likes of this example from the Pragmatic Programmer: ...implement a mini-language to control a simple drawing package... The language consists of single-letter commands. Some commands are followed by a single number. For example, the following input would draw a rectangle: P 2 # select pen 2 D # pen down W 2 # draw west 2cm N 1 # then north 1 E 2 # then east 2 S 1 # then back south U # pen up Thank you!

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Lucene.net create+lock errors in ASP.NET

- by acidzombie24

I have an issue with Lucene.net. It throws a lock exception. After poking around i notice these things. My code below works in an app bit when calling in Application_Start i get a NoSuchDirectoryException. Not closing the writer (as my code doesnt do below) i WILL get a LockObtainFailedException with the message Lock obtain timed out: SimpleFSLock@<FULL_PATH> from either app or asp.net These thread hinted when spawning threads they get less permissions then i do (but! my main thread has problems as well...) and one solution is to impersonate IIS. I am using visual studios 2010. I am not sure how full blown it is but my attempt to impersonate it failed. So my question is how do i have lucene create the directory and not throw an exception if dont close the writer for some reason (such as power going out)? http://stackoverflow.com/questions/2341163/why-is-my-lucene-index-getting-locked/2499285#2499285 http://stackoverflow.com/questions/1123517/lucene-net-and-i-o-threading-issue/1123981#1123981 static IndexWriter writer = null; static void lucene_init() { bool create = false; string dirname = "LuceneIndex_z"; if (System.IO.Directory.Exists(dirname) == false) create = true; var directory = FSDirectory.GetDirectory(dirname); var analyzer = new StandardAnalyzer(); writer = new IndexWriter(directory, analyzer, create); }

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Lucene.net create+lock errors in ASP.NET

- by acidzombie24

I have an issue with Lucene.net. It throws a lock exception. After poking around i notice these things. My code below works in an app bit when calling in Application_Start i get a NoSuchDirectoryException. Not closing the writer (as my code doesnt do below) i WILL get a LockObtainFailedException with the message Lock obtain timed out: SimpleFSLock@<FULL_PATH> from either app or asp.net These thread hinted when spawning threads they get less permissions then i do (but! my main thread has problems as well...) and one solution is to impersonate IIS. I am using visual studios 2010. I am not sure how full blown it is but my attempt to impersonate it failed. So my question is how do i have lucene create the directory and not throw an exception if dont close the writer for some reason (such as power going out)? http://stackoverflow.com/questions/2341163/why-is-my-lucene-index-getting-locked/2499285#2499285 http://stackoverflow.com/questions/1123517/lucene-net-and-i-o-threading-issue/1123981#1123981 static IndexWriter writer = null; static void lucene_init() { bool create = false; //I now use a full path. I still get NoSuchDirectoryException //string dirname = "LuceneIndex_z"; if (System.IO.Directory.Exists(dirname) == false) create = true; var directory = FSDirectory.GetDirectory(dirname); var analyzer = new StandardAnalyzer(); writer = new IndexWriter(directory, analyzer, create); }

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What do I do about recurring billing?

- by phidah

This might be a subjective question, but I'll give it a go. There are already a number of questions on SO that revolves around subscription billing management. I am currently working on a SaaS solution that will require a fully automated billing system. What I am not looking for when asking this question is not advice on implementing towards a specific payment gateway or stuff like that. Instead I'd like advice on what kind of approach to take. The functionality that I need is a system that can handle upgrades, downgrades, recurring billing, cancellations, etc. Initially for one product only, but it might over time be a requirement that the system can handle multiple products (by products I mean fundamentally different products, not different variations of the same product). As I see it there are a number of possible approaches when you need a solution like this: Code a billing server yourself that supports this and is decoupled from each product so that it can handle multiple independent products. Use a hosted solution like Recurly, Chargify, Spreedly or CheddarGetter. The advantage of using a hosted solution is obviously that you don't need PCI certification, the concern is outsourced and it is a lot faster to get up and running. These advantages come at a cost however: The most important support function for your product - i.e. the billing is not in your control. Additionally you have less control and flexibility. What would you do? If we look beyond the PCI requirements I would definately prefer to have a system coded in-house that could do this kind of job. On the other hand I've heard from numerous sources that coding a system like this is a pain. Any advice is highly appreciated. Also, if you advice to code it yourself, any experiences on how to do it or if there are any opensource projects (no matter the language, what I'm after is not the code but the structure) that I can benefit from would really mean alot. Thanks in advance for your inputs! :-)

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InvalidOperationException (Lambda parameter not in scope) when trying to Compile a Lambda Expression

- by Moshe Levi

Hello, I'm writing an Expression Parser to make my API more refactor friendly and less error prone. basicaly, I want the user to write code like that: repository.Get(entity => entity.Id == 10); instead of: repository.Get<Entity>("Id", 10); Extracting the member name from the left side of the binary expression was straight forward. The problems began when I tried to extract the value from the right side of the expression. The above snippet demonstrates the simplest possible case which involves a constant value but it can be much more complex involving closures and what not. After playing with that for some time I gave up on trying to cover all the possible cases myself and decided to use the framework to do all the heavy lifting for me by compiling and executing the right side of the expression. the relevant part of the code looks like that: public static KeyValuePair<string, object> Parse<T>(Expression<Func<T, bool>> expression) { var binaryExpression = (BinaryExpression)expression.Body; string memberName = ParseMemberName(binaryExpression.Left); object value = ParseValue(binaryExpression.Right); return new KeyValuePair<string, object>(memberName, value); } private static object ParseValue(Expression expression) { Expression conversionExpression = Expression.Convert(expression, typeof(object)); var lambdaExpression = Expression.Lambda<Func<object>>(conversionExpression); Func<object> accessor = lambdaExpression.Compile(); return accessor(); } Now, I get an InvalidOperationException (Lambda parameter not in scope) in the Compile line. when I googled for the solution I came up with similar questions that involved building an expression by hand and not supplying all the pieces, or trying to rely on parameters having the same name and not the same reference. I don't think that this is the case here because I'm reusing the given expression. I would appreciate if someone will give me some pointers on this. Thank you.

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C++ Set Erase Entry Question

- by Wallace

Hi. I encountered a problem here. I'm using C++ multiset. This is the test file. Score: 3-1 Ben Steven Score: 1-0 Ben Score: 0-0 Score: 1-1 Cole Score: 1-2 Ben I'm using while loop and ifstream (fin1) to read in from the test file above. multiset<string, less<string> > myset; while(!fin1.eof()) { fin1 >> scoreName; if(scoreName == "Score:") { //calculates number of matches played } else { goalCheck = scoreName.substr(1,1); if(goalCheck == "-") { string lGoal, rGoal; lGoal = scoreName.substr(0,1); rGoal = scoreName.substr(2,1); int leftGoal, rightGoal; leftGoal = atoi(lGoal.c_str()); rightGoal = atoi(rGoal.c_str()); if(leftGoal > rightGoal) //if team wins { //some computations } else if(leftGoal < rightGoal) //if team loses { //computations } else if(leftGoal == rightGoal) //if team draws { //computations } else { myset.insert(myset.begin(), scoreName); } } } I'm inserting all names into myset (regardless of wins/loses/draws) in my last else statement. But I only require the names of those matches who won/draw. Those names whose matches lost will not be included in myset. In the test file above, there's only one match that lost (1-2) and I wanted to remove "Ben". How can I do that? I tried to use myset.erase(), but I'm not sure how to get it point to Ben and remove it from myset. Any help is much appreciated. Thanks.

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