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• How do functional programming languages work?

  - by eSKay

  I was just reading this excellent post, and got some better understanding of what exactly object oriented programming is, how Java implements it in one extreme manner, and how functional programming languages are a contrast. What I was thinking is this: if functional programming languages cannot save any state, how do they do some simple stuff like reading input from a user (I mean how do they "store" it), or storing any data for that matter? For example - how would this simple C thing translate to any functional programming language, for example haskell? #include<stdio.h> int main() { int no; scanf("%d",&no); return 0; }

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• Recursive TreeView in ASP.NET

  - by waqasahmed

  I have an object of type list from which I wish to use to populate a treeview in asp.net c#. Each object item has: id | Name | ParentId so for example: id | Name | ParentId ------------------------- 1 | Alice | 0 2 | Bob | 1 3 | Charlie | 1 4 | David | 2 In the above example, the parent would be Alice having two children Bob and Charlie. David is the child of Bob. I have had many problems trying to dynamically populate the treeview recursively in c# ASP.NET Does any one have a simple solution? Btw: you can use People.Id, People.Name and People.ParentId to access the members since it is an object belonging to list. I can post you my code so far (many attempts made) but not sure how useful it will be.

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• Inside the Concurrent Collections: ConcurrentDictionary

  - by Simon Cooper

  Using locks to implement a thread-safe collection is rather like using a sledgehammer - unsubtle, easy to understand, and tends to make any other tool redundant. Unlike the previous two collections I looked at, ConcurrentStack and ConcurrentQueue, ConcurrentDictionary uses locks quite heavily. However, it is careful to wield locks only where necessary to ensure that concurrency is maximised. This will, by necessity, be a higher-level look than my other posts in this series, as there is quite a lot of code and logic in ConcurrentDictionary. Therefore, I do recommend that you have ConcurrentDictionary open in a decompiler to have a look at all the details that I skip over. The problem with locks There's several things to bear in mind when using locks, as encapsulated by the lock keyword in C# and the System.Threading.Monitor class in .NET (if you're unsure as to what lock does in C#, I briefly covered it in my first post in the series): Locks block threads The most obvious problem is that threads waiting on a lock can't do any work at all. No preparatory work, no 'optimistic' work like in ConcurrentQueue and ConcurrentStack, nothing. It sits there, waiting to be unblocked. This is bad if you're trying to maximise concurrency. Locks are slow Whereas most of the methods on the Interlocked class can be compiled down to a single CPU instruction, ensuring atomicity at the hardware level, taking out a lock requires some heavy lifting by the CLR and the operating system. There's quite a bit of work required to take out a lock, block other threads, and wake them up again. If locks are used heavily, this impacts performance. Deadlocks When using locks there's always the possibility of a deadlock - two threads, each holding a lock, each trying to aquire the other's lock. Fortunately, this can be avoided with careful programming and structured lock-taking, as we'll see. So, it's important to minimise where locks are used to maximise the concurrency and performance of the collection. Implementation As you might expect, ConcurrentDictionary is similar in basic implementation to the non-concurrent Dictionary, which I studied in a previous post. I'll be using some concepts introduced there, so I recommend you have a quick read of it. So, if you were implementing a thread-safe dictionary, what would you do? The naive implementation is to simply have a single lock around all methods accessing the dictionary. This would work, but doesn't allow much concurrency. Fortunately, the bucketing used by Dictionary allows a simple but effective improvement to this - one lock per bucket. This allows different threads modifying different buckets to do so in parallel. Any thread making changes to the contents of a bucket takes the lock for that bucket, ensuring those changes are thread-safe. The method that maps each bucket to a lock is the GetBucketAndLockNo method: private void GetBucketAndLockNo( int hashcode, out int bucketNo, out int lockNo, int bucketCount) { // the bucket number is the hashcode (without the initial sign bit) // modulo the number of buckets bucketNo = (hashcode & 0x7fffffff) % bucketCount; // and the lock number is the bucket number modulo the number of locks lockNo = bucketNo % m_locks.Length; } However, this does require some changes to how the buckets are implemented. The 'implicit' linked list within a single backing array used by the non-concurrent Dictionary adds a dependency between separate buckets, as every bucket uses the same backing array. Instead, ConcurrentDictionary uses a strict linked list on each bucket: This ensures that each bucket is entirely separate from all other buckets; adding or removing an item from a bucket is independent to any changes to other buckets. Modifying the dictionary All the operations on the dictionary follow the same basic pattern: void AlterBucket(TKey key, ...) { int bucketNo, lockNo; 1: GetBucketAndLockNo( key.GetHashCode(), out bucketNo, out lockNo, m_buckets.Length); 2: lock (m_locks[lockNo]) { 3: Node headNode = m_buckets[bucketNo]; 4: Mutate the node linked list as appropriate } } For example, when adding another entry to the dictionary, you would iterate through the linked list to check whether the key exists already, and add the new entry as the head node. When removing items, you would find the entry to remove (if it exists), and remove the node from the linked list. Adding, updating, and removing items all follow this pattern. Performance issues There is a problem we have to address at this point. If the number of buckets in the dictionary is fixed in the constructor, then the performance will degrade from O(1) to O(n) when a large number of items are added to the dictionary. As more and more items get added to the linked lists in each bucket, the lookup operations will spend most of their time traversing a linear linked list. To fix this, the buckets array has to be resized once the number of items in each bucket has gone over a certain limit. (In ConcurrentDictionary this limit is when the size of the largest bucket is greater than the number of buckets for each lock. This check is done at the end of the TryAddInternal method.) Resizing the bucket array and re-hashing everything affects every bucket in the collection. Therefore, this operation needs to take out every lock in the collection. Taking out mutiple locks at once inevitably summons the spectre of the deadlock; two threads each hold a lock, and each trying to acquire the other lock. How can we eliminate this? Simple - ensure that threads never try to 'swap' locks in this fashion. When taking out multiple locks, always take them out in the same order, and always take out all the locks you need before starting to release them. In ConcurrentDictionary, this is controlled by the AcquireLocks, AcquireAllLocks and ReleaseLocks methods. Locks are always taken out and released in the order they are in the m_locks array, and locks are all released right at the end of the method in a finally block. At this point, it's worth pointing out that the locks array is never re-assigned, even when the buckets array is increased in size. The number of locks is fixed in the constructor by the concurrencyLevel parameter. This simplifies programming the locks; you don't have to check if the locks array has changed or been re-assigned before taking out a lock object. And you can be sure that when a thread takes out a lock, another thread isn't going to re-assign the lock array. This would create a new series of lock objects, thus allowing another thread to ignore the existing locks (and any threads controlling them), breaking thread-safety. Consequences of growing the array Just because we're using locks doesn't mean that race conditions aren't a problem. We can see this by looking at the GrowTable method. The operation of this method can be boiled down to: private void GrowTable(Node[] buckets) { try { 1: Acquire first lock in the locks array // this causes any other thread trying to take out // all the locks to block because the first lock in the array // is always the one taken out first // check if another thread has already resized the buckets array // while we were waiting to acquire the first lock 2: if (buckets != m_buckets) return; 3: Calculate the new size of the backing array 4: Node[] array = new array[size]; 5: Acquire all the remaining locks 6: Re-hash the contents of the existing buckets into array 7: m_buckets = array; } finally { 8: Release all locks } } As you can see, there's already a check for a race condition at step 2, for the case when the GrowTable method is called twice in quick succession on two separate threads. One will successfully resize the buckets array (blocking the second in the meantime), when the second thread is unblocked it'll see that the array has already been resized & exit without doing anything. There is another case we need to consider; looking back at the AlterBucket method above, consider the following situation: Thread 1 calls AlterBucket; step 1 is executed to get the bucket and lock numbers. Thread 2 calls GrowTable and executes steps 1-5; thread 1 is blocked when it tries to take out the lock in step 2. Thread 2 re-hashes everything, re-assigns the buckets array, and releases all the locks (steps 6-8). Thread 1 is unblocked and continues executing, but the calculated bucket and lock numbers are no longer valid. Between calculating the correct bucket and lock number and taking out the lock, another thread has changed where everything is. Not exactly thread-safe. Well, a similar problem was solved in ConcurrentStack and ConcurrentQueue by storing a local copy of the state, doing the necessary calculations, then checking if that state is still valid. We can use a similar idea here: void AlterBucket(TKey key, ...) { while (true) { Node[] buckets = m_buckets; int bucketNo, lockNo; GetBucketAndLockNo( key.GetHashCode(), out bucketNo, out lockNo, buckets.Length); lock (m_locks[lockNo]) { // if the state has changed, go back to the start if (buckets != m_buckets) continue; Node headNode = m_buckets[bucketNo]; Mutate the node linked list as appropriate } break; } } TryGetValue and GetEnumerator And so, finally, we get onto TryGetValue and GetEnumerator. I've left these to the end because, well, they don't actually use any locks. How can this be? Whenever you change a bucket, you need to take out the corresponding lock, yes? Indeed you do. However, it is important to note that TryGetValue and GetEnumerator don't actually change anything. Just as immutable objects are, by definition, thread-safe, read-only operations don't need to take out a lock because they don't change anything. All lockless methods can happily iterate through the buckets and linked lists without worrying about locking anything. However, this does put restrictions on how the other methods operate. Because there could be another thread in the middle of reading the dictionary at any time (even if a lock is taken out), the dictionary has to be in a valid state at all times. Every change to state has to be made visible to other threads in a single atomic operation (all relevant variables are marked volatile to help with this). This restriction ensures that whatever the reading threads are doing, they never read the dictionary in an invalid state (eg items that should be in the collection temporarily removed from the linked list, or reading a node that has had it's key & value removed before the node itself has been removed from the linked list). Fortunately, all the operations needed to change the dictionary can be done in that way. Bucket resizes are made visible when the new array is assigned back to the m_buckets variable. Any additions or modifications to a node are done by creating a new node, then splicing it into the existing list using a single variable assignment. Node removals are simply done by re-assigning the node's m_next pointer. Because the dictionary can be changed by another thread during execution of the lockless methods, the GetEnumerator method is liable to return dirty reads - changes made to the dictionary after GetEnumerator was called, but before the enumeration got to that point in the dictionary. It's worth listing at this point which methods are lockless, and which take out all the locks in the dictionary to ensure they get a consistent view of the dictionary: Lockless: TryGetValue GetEnumerator The indexer getter ContainsKey Takes out every lock (lockfull?): Count IsEmpty Keys Values CopyTo ToArray Concurrent principles That covers the overall implementation of ConcurrentDictionary. I haven't even begun to scratch the surface of this sophisticated collection. That I leave to you. However, we've looked at enough to be able to extract some useful principles for concurrent programming: Partitioning When using locks, the work is partitioned into independant chunks, each with its own lock. Each partition can then be modified concurrently to other partitions. Ordered lock-taking When a method does need to control the entire collection, locks are taken and released in a fixed order to prevent deadlocks. Lockless reads Read operations that don't care about dirty reads don't take out any lock; the rest of the collection is implemented so that any reading thread always has a consistent view of the collection. That leads us to the final collection in this little series - ConcurrentBag. Lacking a non-concurrent analogy, it is quite different to any other collection in the class libraries. Prepare your thinking hats!

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• adding errors to Django form errors.__all__

  - by hendrixski

  How do I add errors to the top of a form after I cleaned the data? I have an object that needs to make a REST call to an external app (google maps) as a pre-save condition, and this can fail, which means I need my users to correct the data in the form. So I clean the data and then try to save and add to the form errors if the save doesn't work: if request.method == "POST": #clean form data try: profile.save() return HttpResponseRedirect(reverse("some_page", args=[some.args])) except ValueError: our_form.errors.__all__ = [u"error message goes here"] return render_to_response(template_name, {"ourform": our_form,}, context_instance=RequestContext(request)) This failed to return the error text in my unit-tests (which were looking for it in {{form.non_field_errors}}), and then when I run it through the debugger, the errors had not been added to the forms error dict when they reach the render_to_response line, nor anywhere else in the our_form tree. Why didn't this work? How am I supposed to add errors to the top of a form after it's been cleaned?

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• Sub-classing TreeView in WinForms for mouse over tool tips

  - by Matt

  Ok, this is a weird one. The expected behaviour for a TreeView control is that, if ShowNodeToolTips is set to false, then, when a label for a tree node exceeds the width of the control (or, more accurately, it's right hand edge is past the right hand edge of the client area), then a tooltip is shown above the node showing the full item's text. I'd like to disable that, because the above semantic doesn't always work, depending on what the treeview is contained within. So I have rolled my own, and got the tooltips to work (and line up better than the default one!) - but I would like to be able to disable the 'default' behaviour for situations where it would work natively. So, can anyone point me in the right direction as to which message to post to the TreeView in order to disable that behaviour? I have looked at the windows control reference, but couldn't find anything that looked like it might be the one.

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• How can I make two "user" editable areas in Wordpress?

  - by thatryan

  Hi all, is there a way to have two posting areas in Wordpress, for clients who can not go into any HTML? Basically the template has 3 columns. One is vertical nav, thats no prob. Second is like a "sidebar" but where the main post will go, a skinny column. Third is large, "main area" size, but will also be user editable content. Does that make sense? Has anyone done something like this before? Thank you.

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• How does the timeout work in Restlet's client class?

  - by Greg Noe

  Here's some code: Client client = new Client(Protocol.HTTP); client.setConnectTimeout(1); //milliseconds Response response = client.post(url, paramRepresentation); System.out.println("timed out"); What I would expect to happen is that it prints "timed out" before the resource has time to process. Instead, nothing happens with the timeout and it doesn't print "timed out" until after the resource returns. Even if I put a Thread.sleep(5000) at the resource that's handling the request, the entire sleep is performed, like the timeout did nothing. Anyone have experience with this? I'm using Restlet 1.1.1. Thanks.

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• Using Logger Filter with Not Equal condition Log4net

  - by Mubashar Ahmad

  Dears I am using log4net in my c# application i have different logger which insert text lines in my single log file. But now i wanted to add a new logger which should not post log entries in the same file rather i should log in a different file so i configured a new fileAppender, After doing whatever i found on the net i am able to create a different file for my new logger but it echoes the same value in first log file too. so please if anybody knows about the use of LogFilters so that i could add "Logger < New logger " match in previously configured appender. Regards Mubashar

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• How do I edit a "ell in an MFC Listbox?

  - by Pedro

  I have CListBox control that has 2 columns and any number of rows. I want the user to be able to click(or maybe double-click) a "cell" and be able edit the text therein. link text (Can't post images yet, need +10). What I mean is that I want to be able to click and edit any of the places where it says "TEST" by clicking on the text to make it editable. How should I go about this? I suppose I should use a mouse click event but how would I make the cell editable?

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• Verification GetHashCode and Equals

  - by nettguy

  Does the following code show the correct implementation of overriding GetHashCode ? public class Person { public string fName{get;set;} public string lName { get; set; } public int age { get; set; } public override bool Equals(object obj) { Person p = obj as Person; if (p == null) return false; return ( p.GetType()==this.GetType() && p.fName==this.fName &&p.lName==this.lName && p.age==this.age ); } //I took the below code from Marc Gravell's post,I am not sure whether i have implemented it properly public override int GetHashCode() { unchecked { int hash = 13; hash = (hash * 7) + fName.GetHashCode(); hash = (hash * 7) + lName.GetHashCode(); hash = (hash * 7) + age.GetHashCode(); return hash; } } }

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• Some instruction needed for PHP OOPS concepts.

  - by Avinash

  Hi, I need to clear some OOPS concepts in PHP. 1) Which is faster $this-method(); or self:method(); 2) I know the concept of static keyword but can you please post the actual Use of it. Since it can not be accessed by the instance, but is there ant benefit for that? 3) what is factory? How can i use it? 4) What is singleton? How can i use that? 5) What is late static binding? http://www.php.net/manual/en/oop5.intro.php I have gone through below link but I am not getting clear with it. Thanks Avinash

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• jqgrid ASP.NET MVC -- getting data right for the grid.

  - by SamM09

  Here is my dilemma, I have not been able to manipulate my data to a form fitting to jqgrid standards. This is my first time using the jqgrid and I've spent a lot of time reading up on it. My js code is as follows: jQuery("#list").jqGrid({ url: '/Home/ListContacts/', dataType: "json", contentType: "application/json; charset=utf-8", mtype: 'POST', colNames: ['First Name', 'MI', 'Last Name'], colModel: [ { name: 'First Name', index: 'FName', width: 40, align: 'left' }, { name: 'MI', index: 'MInitial', width: 40, align: 'left' }, { name: 'Last Name', index: 'LName', width: 400, align: 'left'}], pager: jQuery('#pager'), rowNum: 10, rowList: [5, 10, 20, 50], sortname: 'Id', sortorder: "desc", repeatitems: false, viewrecords: true, imgpath: '/scripts/themes/basic/images', caption: 'My first grid' }); }); what im getting from the database: [["4","Jenna","Mccarthy"],["56","wer","weoiru"]] Now correct me if I am wrong, but the index: in my colModel refers to the column names in my database right? Could someone point to a reference that is straight forward or just start me off with this I would be most grateful.

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• How can I make the modal popup scroll its contents with the page?

  - by Middletone

  I've got a modal popup and when it loads contents that are taller than the browser height I am unable to scroll down to view the rest of the information. Instead the background can scroll but the popup won't. Instead I'd like to have the popup stay put and when the user scrolls up or down it leave the popup in place and let them scroll to the bottom of the contents. If you make a super long post on Facebook the popup works correctly and I'd like to know how I can get this same effect with this control.

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• Can you handle both json and html datatypes in the same ajax call?

  - by Prabhu

  Is there anyway I can handle both json and html return types when posting jquery ajax: For example, this ajax call expects html back $.ajax({ type: "POST", url: url data: data, dataType: "html", success: function (response) { var $html = "<li class='list-item'>" + response + "</li>"; $('#a').prepend($html); }, error: function (xhr, status, error) { alert(xhr.statusText); } }); but I wanted to modify it so that I can return a json object if there is a model error. so I can do something like this: success: function (response) { if (response.Error){ alert(response.Message); } else { var $html = "<li class='list-item'>" + response + "</li>"; $('#a').prepend($html); } Is this possible?

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• make RMI Stub with netBeans

  - by park

  I see some where in the web that we can make Stub dynamically with Netbeans and it`s a good feature of it. I search a lot but all hits are from Old version (4 or 5) and others told a complete reference is in Netbeans website but the links is removed and i couldn`t find it in the site. Broken Link : rmi.netbeans.org Please if there is way which i don`t know tell me or there is not let me know for not search any more and try to work with rmic. more search results : http://forums.sun.com/thread.jspa?threadID=5037503 http://forums.netbeans.org/post-8076.html&highlight= Thanks

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• PublishPost method example for Actionscript API Facebook connect required

  - by freddelm

  I established an extended permission with Facebook connect, works like a charm, but i just can't seem to publish messages on my wall. i keep getting this error: error code 100: Invalid parameter my code: var message:String = "test facebookconnect"; var publishpost:PublishPost = new PublishPost(message, null, null, null); publishpost.addEventListener(FacebookEvent.COMPLETE, function(e:FacebookEvent) { MonsterDebugger.trace(this, e); }); publishpost.addEventListener(FacebookEvent.ERROR, function(e:FacebookEvent) { MonsterDebugger.trace(this, e); }); publishpost.addEventListener(FacebookEvent.CONNECT, function(e:FacebookEvent) { MonsterDebugger.trace(this, e); }); fldFacebook.post(publishpost); Any clear examples/tutorials would help a lot in how to use this publishpost with the actionscript API thanks in advance.

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• Good Guide For Web App Security?

  - by QAH

  Hello! I am pretty good on making web applications and I know how to transfer data to and from client/server, etc. I need some help though learning how to make the data exchanges more secure. That is the reason why I feel kind of scared to publish any web app I make. I wanted to know what are some good guides to help you understand and learn how to secure data transfer with your web application? Things like better authentication for example and making better logins. You can post any suggestion, but just for your information, I mainly code my web apps with Javascript and PHP. Also, I transfer my data using JSON or XML. Thanks a lot

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• Xcode license agreement different than Apple Developer Agreement?

  - by longpine

  The Apple Developer Agreement (on their website when signing up for a developer account) says: "Apple reserves the right, at its discretion, to modify this Agreement, including any rules and policies at any time." And also: "You agree to follow Apple's Guidelines For Using Apple Trademarks and Copyrights as published on Apple's website at www.apple.com/legal/guidelinesfor3rdparties.html ("Guidelines") and as may be modified from time to time." If I buy a Mac with OS X, it comes with Xcode, correct? In that case what does the license agreement for Xcode say? Does it contain the clauses above, or anything similar? If anyone wants to post a copy of the license agreement here, that would be helpful, but I'm not sure if copyright would allow that.

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• Struts2 <s:bean/> tag, used to instanciate a Parametric Bean

  - by Rasatavohary

  Hi, After looking a while other google, and the web, I decided to post my question here. The question is quite really basic, and simple : How do I use the struts2 tag <s:bean ... /> to instanciate a Parametric Bean ? For example imagine I have : public class GenericBean<T> { ... How will I instanciate this bean with a BeanType for instance, inside a jsp using struts 2 ? <s:bean name="GenericBean" var="myBean"/> Thanks you.

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• Comparison of Code Review Tools/Systems

  - by SytS

  There are a number of tools/systems available aimed at streamlining and enhancing the code review process, including: CodeStriker Review Board, code review system in use at VMWare Code Collaborator, commercial product by SmartBear Rietveld, based on Modrian, the code review system in use at Google Crucible, commercial product by Atlassian These systems all have varying feature sets, and differ in degrees of maturity and polish; the selection is a little bewildering for someone who is evaluating code review systems for the frist time. Some of these tools have already been mentioned in other questions/answers on StackOverflow, but I would like to see a more comprehensive comparison of the more popular systems, especially with respect to: integration with source control systems integration with bug tracking systems supported workflow (reviews pre/post commit, review or contiguous/non-contigous revision ranges, etc) deployment/maintenance requirements

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• SqlDateTime overflow thrown by Typed DataSet Insert

  - by end-user

  I'm using a Typed DataSet with an Insert statement; I have a table that has a smalldatetime field defined to accept null values. When I insert from a .NET 2.0 FormView, I get a "SqlDateTime overflow. Must be between 1/1/1753 12:00:00 AM and 12/31/9999 11:59:59 PM." Now, I've read this post, and the parameter as sent to the class constructor is defined as global::System.Nullable<global::System.DateTime> DoB So, it looks like it should accept a Nullable obj. Additionally, the generated code is testing the value sent. if ((DoB.HasValue == true)) { command.Parameters[6].Value = ((System.DateTime)(DoB.Value)); } else { command.Parameters[6].Value = global::System.DBNull.Value; } Specifically, the error is occurring when generated SqlClient.SqlCommand.ExecuteScalar() runs: try { returnValue = command.ExecuteScalar(); } So, I guess my question is: how do I use a Typed DataSet to set a blank value (passed from a FormView on CommandName=Insert) to a null in a database?

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• R Package Installation with Oracle R Enterprise

  - by Sherry LaMonica-Oracle

  Normal 0 false false false EN-US X-NONE X-NONE Programming languages give developers the opportunity to write reusable functions and to bundle those functions into logical deployable entities. In R, these are called packages. R has thousands of such packages provided by an almost equally large group of third-party contributors. To allow others to benefit from these packages, users can share packages on the CRAN system for use by the vast R development community worldwide. R's package system along with the CRAN framework provides a process for authoring, documenting and distributing packages to millions of users. In this post, we'll illustrate the various ways in which such R packages can be installed for use with R and together with Oracle R Enterprise. In the following, the same instructions apply when using either open source R or Oracle R Distribution. In this post, we cover the following package installation scenarios for: R command line Linux shell command line Use with Oracle R Enterprise Installation on Exadata or RAC Installing all packages in a CRAN Task View Troubleshooting common errors 1. R Package Installation BasicsR package installation basics are outlined in Chapter 6 of the R Installation and Administration Guide. There are two ways to install packages from the command line: from the R command line and from the shell command line. For this first example on Oracle Linux using Oracle R Distribution, we’ll install the arules package as root so that packages will be installed in the default R system-wide location where all users can access it, /usr/lib64/R/library.Within R, using the install.packages function always attempts to install the latest version of the requested package available on CRAN:R> install.packages("arules")If the arules package depends upon other packages that are not already installed locally, the R installer automatically downloads and installs those required packages. This is a huge benefit that frees users from the task of identifying and resolving those dependencies.You can also install R from the shell command line. This is useful for some packages when an internet connection is not available or for installing packages not uploaded to CRAN. To install packages this way, first locate the package on CRAN and then download the package source to your local machine. For example:$ wget http://cran.r-project.org/src/contrib/arules_1.1-2.tar.gz Then, install the package using the command R CMD INSTALL:$ R CMD INSTALL arules_1.1-2.tar.gzA major difference between installing R packages using the R package installer at the R command line and shell command line is that package dependencies must be resolved manually at the shell command line. Package dependencies are listed in the Depends section of the package’s CRAN site. If dependencies are not identified and installed prior to the package’s installation, you will see an error similar to:ERROR: dependency ‘xxx’ is not available for package ‘yyy’As a best practice and to save time, always refer to the package’s CRAN site to understand the package dependencies prior to attempting an installation. If you don’t run R as root, you won’t have permission to write packages into the default system-wide location and you will be prompted to create a personal library accessible by your userid. You can accept the personal library path chosen by R, or specify the library location by passing parameters to the install.packages function. For example, to create an R package repository in your home directory: R> install.packages("arules", lib="/home/username/Rpackages")or$ R CMD INSTALL arules_1.1-2.tar.gz --library=/home/username/RpackagesRefer to the install.packages help file in R or execute R CMD INSTALL --help at the shell command line for a full list of command line options.To set the library location and avoid having to specify this at every package install, simply create the R startup environment file .Renviron in your home area if it does not already exist, and add the following piece of code to it:R_LIBS_USER = "/home/username/Rpackages" 2. Setting the RepositoryEach time you install an R package from the R command line, you are asked which CRAN mirror, or server, R should use. To set the repository and avoid having to specify this during every package installation, create the R startup command file .Rprofile in your home directory and add the following R code to it:cat("Setting Seattle repository")r = getOption("repos") r["CRAN"] = "http://cran.fhcrc.org/"options(repos = r)rm(r) This code snippet sets the R package repository to the Seattle CRAN mirror at the start of each R session. 3. Installing R Packages for use with Oracle R EnterpriseEmbedded R execution with Oracle R Enterprise allows the use of CRAN or other third-party R packages in user-defined R functions executed on the Oracle Database server. The steps for installing and configuring packages for use with Oracle R Enterprise are the same as for open source R. The database-side R engine just needs to know where to find the R packages.The Oracle R Enterprise installation is performed by user oracle, which typically does not have write permission to the default site-wide library, /usr/lib64/R/library. On Linux and UNIX platforms, the Oracle R Enterprise Server installation provides the ORE script, which is executed from the operating system shell to install R packages and to start R. The ORE script is a wrapper for the default R script, a shell wrapper for the R executable. It can be used to start R, run batch scripts, and build or install R packages. Unlike the default R script, the ORE script installs packages to a location writable by user oracle and accessible by all ORE users - $ORACLE_HOME/R/library.To install a package on the database server so that it can be used by any R user and for use in embedded R execution, an Oracle DBA would typically download the package source from CRAN using wget. If the package depends on any packages that are not in the R distribution in use, download the sources for those packages, also.  For a single Oracle Database instance, replace the R script with ORE to install the packages in the same location as the Oracle R Enterprise packages. $ wget http://cran.r-project.org/src/contrib/arules_1.1-2.tar.gz$ ORE CMD INSTALL arules_1.1-2.tar.gzBehind the scenes, the ORE script performs the equivalent of setting R_LIBS_USER to the value of $ORACLE_HOME/R/library, and all R packages installed with the ORE script are installed to this location. For installing a package on multiple database servers, such as those in an Oracle Real Application Clusters (Oracle RAC) or a multinode Oracle Exadata Database Machine environment, use the ORE script in conjunction with the Exadata Distributed Command Line Interface (DCLI) utility.$ dcli -g nodes -l oracle ORE CMD INSTALL arules_1.1-1.tar.gz The DCLI -g flag designates a file containing a list of nodes to install on, and the -l flag specifies the user id to use when executing the commands. For more information on using DCLI with Oracle R Enterprise, see Chapter 5 in the Oracle R Enterprise Installation Guide.If you are using an Oracle R Enterprise client, install the package the same as any R package, bearing in mind that you must install the same version of the package on both the client and server machines to avoid incompatibilities. 4. CRAN Task ViewsCRAN also maintains a set of Task Views that identify packages associated with a particular task or methodology. Task Views are helpful in guiding users through the huge set of available R packages. They are actively maintained by volunteers who include detailed annotations for routines and packages. If you find one of the task views is a perfect match, you can install every package in that view using the ctv package - an R package for automating package installation. To use the ctv package to install a task view, first, install and load the ctv package.R> install.packages("ctv")R> library(ctv)Then query the names of the available task views and install the view you choose.R> available.views() R> install.views("TimeSeries") 5. Using and Managing R packages To use a package, start up R and load packages one at a time with the library command.Load the arules package in your R session. R> library(arules)Verify the version of arules installed.R> packageVersion("arules")[1] '1.1.2'Verify the version of arules installed on the database server using embedded R execution.R> ore.doEval(function() packageVersion("arules"))View the help file for the apropos function in the arules packageR> ?aproposOver time, your package repository will contain more and more packages, especially if you are using the system-wide repository where others are adding additional packages. It’s good to know the entire set of R packages accessible in your environment. To list all available packages in your local R session, use the installed.packages command:R> myLocalPackages <- row.names(installed.packages())R> myLocalPackagesTo access the list of available packages on the ORE database server from the ORE client, use the following embedded R syntax: R> myServerPackages <- ore.doEval(function() row.names(installed.packages()) R> myServerPackages 6. Troubleshooting Common ProblemsInstalling Older Versions of R packagesIf you immediately upgrade to the latest version of R, you will have no problem installing the most recent versions of R packages. However, if your version of R is older, some of the more recent package releases will not work and install.packages will generate a message such as: Warning message: In install.packages("arules") : package ‘arules’ is not availableThis is when you have to go to the Old sources link on the CRAN page for the arules package and determine which version is compatible with your version of R.Begin by determining what version of R you are using:$ R --versionOracle Distribution of R version 3.0.1 (--) -- "Good Sport" Copyright (C) The R Foundation for Statistical Computing Platform: x86_64-unknown-linux-gnu (64-bit)Given that R-3.0.1 was released May 16, 2013, any version of the arules package released after this date may work. Scanning the arules archive, we might try installing version 0.1.1-1, released in January of 2014:$ wget http://cran.r-project.org/src/contrib/Archive/arules/arules_1.1-1.tar.gz$ R CMD INSTALL arules_1.1-1.tar.gzFor use with ORE:$ ORE CMD INSTALL arules_1.1-1.tar.gzThe "package not available" error can also be thrown if the package you’re trying to install lives elsewhere, either another R package site, or it’s been removed from CRAN. A quick Google search usually leads to more information on the package’s location and status.Oracle R Enterprise is not in the R library pathOn Linux hosts, after installing the ORE server components, starting R, and attempting to load the ORE packages, you may receive the error:R> library(ORE)Error in library(ORE) : there is no package called ‘ORE’If you know the ORE packages have been installed and you receive this error, this is the result of not starting R with the ORE script. To resolve this problem, exit R and restart using the ORE script. After restarting R and ">running the command to load the ORE packages, you should not receive any errors.$ ORER> library(ORE)On Windows servers, the solution is to make the location of the ORE packages visible to R by adding them to the R library paths. To accomplish this, exit R, then add the following lines to the .Rprofile file. On Windows, the .Rprofile file is located in R\etc directory C:\Program Files\R\R-<version>\etc. Add the following lines:.libPaths("<path to $ORACLE_HOME>/R/library")The above line will tell R to include the R directory in the Oracle home as part of its search path. When you start R, the path above will be included, and future R package installations will also be saved to $ORACLE_HOME/R/library. This path should be writable by the user oracle, or the userid for the DBA tasked with installing R packages.Binary package compiled with different version of RBy default, R will install pre-compiled versions of packages if they are found. If the version of R under which the package was compiled does not match your installed version of R you will get an error message:Warning message: package ‘xxx’ was built under R version 3.0.0The solution is to download the package source and build it for your version of R.$ wget http://cran.r-project.org/src/contrib/Archive/arules/arules_1.1-1.tar.gz$ R CMD INSTALL arules_1.1-1.tar.gzFor use with ORE:$ ORE CMD INSTALL arules_1.1-1.tar.gzUnable to execute files in /tmp directoryBy default, R uses the /tmp directory to install packages. On security conscious machines, the /tmp directory is often marked as "noexec" in the /etc/fstab file. This means that no file under /tmp can ever be executed, and users who attempt to install R package will receive an error:ERROR: 'configure' exists but is not executable -- see the 'R Installation and Administration Manual’The solution is to set the TMP and TMPDIR environment variables to a location which R will use as the compilation directory. For example:$ mkdir <some path>/tmp$ export TMPDIR= <some path>/tmp$ export TMP= <some path>/tmpThis error typically appears on Linux client machines and not database servers, as Oracle Database writes to the value of the TMP environment variable for several tasks, including holding temporary files during database installation. 7. Creating your own R packageCreating your own package and submitting to CRAN is for advanced users, but it is not difficult. The procedure to follow, along with details of R's package system, is detailed in the Writing R Extensions manual.

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• Custom Events in pygame

  - by SapphireSun

  Hello everyone, I'm having trouble getting my custom events to fire. My regular events work fine, but I guess I'm doing something wrong. Here is the relevant code: evt = pygame.event.Event(gui.INFOEVENT, {'time':time,'freq':freq,'db':db}) print "POSTING", evt pygame.event.post(evt) .... Later .... for event in pygame.event.get(): print "GOT", event if event.type == pygame.QUIT: sys.exit() dispatcher.dispatch(event) gui.INFOEVENT = 101 by the way. The POSTING print statement fires, but the GOT one never shows my event. Thanks!

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• Retrieve object from jquery in php script

  - by majc

  I'm trying to rebuild an object encoded with Json but i'm not getting any value. JQuery: $.post("views/insert_tasks.php",{ clickedRows : clickrows , <?php echo "tasks:'" . json_encode($tasks) . "'"; ?> }, function(data) { }); this is the PHPcode to retrieve the object: $tasks = json_decode(stripslashes($_POST['tasks']), true); $tasks is empty after execute the code above. This is what I'm getting with the $_POST['tasks']: [{"task_id":"1","description":"<p>Fazer heroi</p>","createdat":"Saturday 22nd of May 2010 11:37:37 PM","createdby":"Miguel Cardoso","max_requests":"2","max_duration":"5","job_id":"Concept Artist"},{"task_id":"2","description":"<p>teste2</p>","createdat":"Sunday 23rd of May 2010 11:23:55 AM","createdby":"Miguel Cardoso","max_requests":"2","max_duration":"5","job_id":"3D Modeller"},{"task_id":"3","description":"<p>teste3</p>","createdat":"Sunday 23rd of May 2010 11:45:39 AM","createdby":"Miguel Cardoso","max_requests":"1","max_duration":"10","job_id":"Writer"}] What I'm doing wrong?

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• change form action from aspx page to master page behind it

  - by ferrer

  i have a master page and a child aspx page, coneected to each other. the master page has the form in it. Now the child page has checkboxes, whose value i would like to pass to another child page with same master page behind it. Can i change the action=abc.aspx and method=post? How can i send all the checkbox values (checkbox.text = [email protected]) to the next page? there are lots of these values that need to pass to nex tpage.

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