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  • What's the difference between these two calls to a function taking a collection of structural types?

    - by James Moore
    Why does the call to fn(Iterator("foo") compile, but the call to fn(fooIterator) fail with an error "type mismatch; found : Iterator[java.lang.String] required: scala.Iterator[com.banshee.Qx.HasLength]" object Qx { type HasLength = {def length: Int} def fn(xs: Iterator[HasLength]) = 3 var tn = fn(Iterator("foo")) var fooIterator = Iterator("foo") var tnFails = fn(fooIterator) //doesn't compile } Aren't they the same thing?

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  • How to lowercase every element of a collection efficiently?

    - by Chris
    Whats the most efficient way to lower case every element of a list or set? My idea for a List: final List<String> strings = new ArrayList<String>(); strings.add("HELLO"); strings.add("WORLD"); for(int i=0,l=strings.size();i<l;++i) { strings.add(strings.remove(0).toLowerCase()); } is there a better, faster way? How would this exmaple look like for a set? As there is currently no method for applying an operation to each element of a set (or list) can it be done without creating an additional temporary set? Something like this would be nice: Set<String> strings = new HashSet<String>(); strings.apply( function (element) { this.replace(element, element.toLowerCase();) } ); Thanks,

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  • How to use a class's type as the type argument for an inherited collection property in C#

    - by Edelweiss Peimann
    I am trying to create a representation of various types of card that inherit from a generic card class and which all contain references to their owning decks. I tried re-declaring them, as suggested here, but it still won't convert to the specific card type. The code I currently have is as such: public class Deck<T> : List<T> where T : Card { void Shuffle() { throw new NotImplementedException("Shuffle not yet implemented."); } } public class Card { public Deck<Card> OwningDeck { get; set; } } public class FooCard : Card { public Deck<FooCard> OwningDeck { get { return (Deck<FooCard>)base.OwningDeck; } set { OwningDeck = value; } } } The compile-time error I am getting: Error 2 Cannot convert type 'Game.Cards.Deck' to 'Game.Cards.Deck' And a warning suggesting I use a new operator to specify that the hiding is intentional. Would doing so be a violation of convention? Is there a better way? My question to stackoverflow is this: Can what I am trying to do be done elegantly in the .NET type system? If so, can some examples be provided?

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  • How to implement a collection (list, map?) of complicated strings in Java?

    - by Alex Cheng
    Hi all. I'm new here. Problem -- I have something like the following entries, 1000 of them: args1=msg args2=flow args3=content args4=depth args6=within ==> args5=content args1=msg args2=flow args3=content args4=depth args6=within args7=distance ==> args5=content args1=msg args2=flow args3=content args6=within ==> args5=content args1=msg args2=flow args3=content args6=within args7=distance ==> args5=content args1=msg args2=flow args3=flow ==> args4=flowbits args1=msg args2=flow args3=flow args5=content ==> args4=flowbits args1=msg args2=flow args3=flow args6=depth ==> args4=flowbits args1=msg args2=flow args3=flow args6=depth ==> args5=content args1=msg args2=flow args4=depth ==> args3=content args1=msg args2=flow args4=depth args5=content ==> args3=content args1=msg args2=flow args4=depth args5=content args6=within ==> args3=content args1=msg args2=flow args4=depth args5=content args6=within args7=distance ==> args3=content I'm doing some sort of suggestion method. Say, args1=msg args2=flow args3=flow == args4=flowbits If the sentence contains msg, flow, and another flow, then I should return the suggestion of flowbits. How can I go around doing it? I know I should scan (whenever a character is pressed on the textarea) a list or array for a match and return the result, but, 1000 entries, how should I implement it? I'm thinking of HashMap, but can I do something like this? <"msg,flow,flow","flowbits" Also, in a sentence the arguments might not be in order, so assuming that it's flow,flow,msg then I can't match anything in the HashMap as the key is "msg,flow,flow". What should I do in this case? Please help. Thanks a million!

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  • Rails form helpers: how to add an element to a collection?

    - by Laran Evans
    I have a keychain object. keychain has_many credentials. I'm trying to write the view code to add a new credential to a keychain. This is the code I have: <% form_for(@keychain) do |f| % <tr <td<%= f.select "credentials[]", current_account.services.collect{ |s| [s.friendly_name, s.id] } %</td <td<%= f.text_field 'credentials', :username %</td <td<%= f.password_field 'credentials', :password %</td </tr <% end % But it fails with this message: NoMethodError in Keychains#new Showing app/views/keychains/_keychain_form.html.erb where line #32 raised: undefined method `credentials[]' for # What am I doing wrong?

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  • Cant we use a Set or collection as a return type in GAE?

    - by user273422
    In my code i have used Set<Employees> as a return type to my function addEmp(). So, i m gettin an Compilation error. The Error is: Compiling module com.employeedepartmentgae.Employeedepartmentgae Refreshing module from source Validating newly compiled units Removing units with errors [ERROR] Errors in 'file:/home/wissen18/employeedepartmentgae/src/com/employeedepartmentgae/client/GreetingServiceAsync.java' [ERROR] Line 6: The import com.employeedepartmentgae.server.domainobject.Employee cannot be resolved [ERROR] Line 18: Employee cannot be resolved to a type [ERROR] Errors in 'file:/home/wissen18/employeedepartmentgae/src/com/employeedepartmentgae/client/GreetingService.java' [ERROR] Line 6: The import com.employeedepartmentgae.server.domainobject.Employee cannot be resolved [ERROR] Line 20: Employee cannot be resolved to a type [ERROR] Errors in 'file:/home/wissen18/employeedepartmentgae/src/com/employeedepartmentgae/client/EmployeeWidget.java' [ERROR] Line 12: The import com.employeedepartmentgae.server.domainobject.Employee cannot be resolved [ERROR] Line 75: The method addEmp(String, String, String, AsyncCallback) from the type GreetingServiceAsync refers to the missing type Employee [ERROR] Line 75: The type new AsyncCallback(){} must implement the inherited abstract method AsyncCallback.onSuccess(Set) [ERROR] Line 75: Employee cannot be resolved to a type [ERROR] Line 94: The method onSuccess(Set) of type new AsyncCallback(){} must override or implement a supertype method [ERROR] Line 94: Employee cannot be resolved to a type [ERROR] Line 96: Employee cannot be resolved to a type [ERROR] Line 96: Employee cannot be resolved to a type [ERROR] Line 98: Employee cannot be resolved to a type Removing invalidated units [WARN] Compilation unit 'file:/home/wissen18/employeedepartmentgae/src/com/employeedepartmentgae/client/Employeedepartmentgae.java' is removed due to invalid reference(s): [WARN] file:/home/wissen18/employeedepartmentgae/src/com/employeedepartmentgae/client/EmployeeWidget.java [WARN] Compilation unit 'file:/home/wissen18/employeedepartmentgae/src/com/employeedepartmentgae/client/DepartmentWidget.java' is removed due to invalid reference(s): [WARN] file:/home/wissen18/employeedepartmentgae/src/com/employeedepartmentgae/client/GreetingService.java [WARN] file:/home/wissen18/employeedepartmentgae/src/com/employeedepartmentgae/client/GreetingServiceAsync.java Computing all possible rebind results for 'com.employeedepartmentgae.client.Employeedepartmentgae' Rebinding com.employeedepartmentgae.client.Employeedepartmentgae Checking rule [ERROR] Unable to find type 'com.employeedepartmentgae.client.Employeedepartmentgae' [ERROR] Hint: Previous compiler errors may have made this type unavailable [ERROR] Hint: Check the inheritance chain from your module; it may not be inheriting a required module or a module may not be adding its source path entries properly So please help me.....

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  • What collection object is appropriate for fixed ordering of values?

    - by makerofthings7
    Scenario: I am tracking several performance counters and have a CounterDescription[] correlate to DataSnapshot[]... where CounterDescription[n] describes the data loaded within DataSnapshot[n]. I want to expose an easy to use API within C# that will allow for the easy and efficient expansion of the arrays. For example CounterDescription[0] = Humidity; DataSnapshot[0] = .9; CounterDescription[1] = Temp; DataSnapshot[1] = 63; My upload object is defined like this: Note how my intent is to correlate many Datasnapshots with a dattime reference, and using the offset of the data to refer to its meaning. This was determined to be the most efficient way to store the data on the back-end, and has now reflected itself into the following structure: public class myDataObject { [DataMember] public SortedDictionary<DateTime, float[]> Pages { get; set; } /// <summary> /// An array that identifies what each position in the array is supposed to be /// </summary> [DataMember] public CounterDescription[] Counters { get; set; } } I will need to expand each of these arrays (float[] and CounterDescription[] ), but whatever data already exists must stay in that relative offset. Which .NET objects support this? I think Array[] , LinkedList<t>, and List<t> Are able to keep the data fixed in the right locations. What do you think?

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  • Iteration through the HtmlDocument.All collection stops at the referenced stylesheet?

    - by Jonas
    Since "bug in .NET" is often not the real cause of a problem, I wonder if I'm missing something here. What I'm doing feels pretty simple. I'm iterating through the elements in a HtmlDocument called doc like this: System.Diagnostics.Debug.WriteLine("*** " + doc.Url + " ***"); foreach (HtmlElement field in doc.All) System.Diagnostics.Debug.WriteLine(string.Format("Tag = {0}, ID = {1} ", field.TagName, field.Id)); I then discovered the debug window output was this: Tag = !, ID = Tag = HTML, ID = Tag = HEAD, ID = Tag = TITLE, ID = Tag = LINK, ID = ... when the actual HTML document looks like this: <!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN"> <html> <head> <title>Protocol</title> <link rel="Stylesheet" type="text/css" media="all" href="ProtocolStyle.css"> </head> <body onselectstart="return false"> <table> <!-- Misc. table elements and cell values --> </table> </body> </html> Commenting out the LINK tag solves the issue for me, and the document is completely parsed. The ProtocolStyle.css file exist on disk and is loaded properly, if that would matter. Is this a bug in .NET 3.5 SP1, or what? For being such a web-oriented framework, I find it hard to believe there would be such a major bug in it.

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  • Why is my emit not getting called?

    - by cRaZiRiCaN
    The client and server connect just fine. For some reason the emit on my client is not firing correctly. I am trying to get the testEmit and testEmit2 working. This is my server: express = require 'express' mongo = require 'mongodb' app = express() server = (require 'http').createServer(app) io = (require 'socket.io').listen(server) server.listen(8080) app.use(express.static(__dirname + '/public')) # db = new mongo.Db("documentsdb", new mongo.Server("localhost", 27017, auto_reconnect: true), {safe:true}) io.sockets.on 'connection', (socket) -> console.log 'Socket.io is connected!' #This returns an array of documents sorted via date by decreasing order. (Most recent documents first.) socket.on 'loadRecentDocuments', -> console.log 'Loading most recent documents.' db.collection 'documents', (err, collection) -> collection.find().sort(dateAdded: -1).toArray (err, documents) -> #This emit is recieved at index.html where a javascript function sendDocuments manages the documents. socket.emit 'sendDocuments', documents return #The index.html provides the code data from the search box via a javascript. io.sockets.on 'findDocuments', (code) -> #Returns an array of documents with the corresponding class code. documentCodeToSearch = code console.log 'Retreaving documents with code: ' + documentCodeToSearch db.collection 'documents', (err, collection) -> collection.find(code:documentCodeToSearch).toArray (err, documents) -> socket.emit 'sendDocuments', documents return #Uploads a document to the server. documentData is sent via javascript from submit.html io.sockets.on 'addDocument', (documentData) -> console.log 'Adding document: ' + documentData db.collection 'documents', (err, collection) -> collection.insert documentData, safe: true return #Test socket.io io.sockets.on 'testEmit', -> console.log('Emit recieved.') socket.emit 'testEmit2', 'caca' return app.listen 1337 console.log "Listening on port 1337..." This is my client: <!doctype HTML> <html> <head> <title>ProjectShare</title> <script src="http://localhost:8080/socket.io/socket.io.js"></script> <script src = "http://ajax.googleapis.com/ajax/libs/jquery/1.8.2/jquery.min.js"></script> <script> //Make sure DOM is ready before mucking around. $(document).ready(function() { console.log('jQuery entered!'); var socket = io.connect('http://localhost:8080'); socket.emit('testEmit'); socket.on('testEmit2', function(data) { console.log('Emit recieved at browser.'); console.log(data); }); console.log('jQuery exit.'); }); </script> </head> <body> <ol> <li><a href="index.html">ProjectShare</a></li> <li><a href="guidelines.html">Guidelines</a></li> <li><a href="upload.html">Upload</a></li> <li> <form> <input type = "search" placeholder = "enter class code"/> <input type = "submit" value = "Go"/> </form> </li> </ol> <ol id = "documentList"> </ol> </body> </html>

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  • How to get a collection of divs with jquery?

    - by Gal Miller
    I want to get the second img: <form id="formElem" name="formElem" action="" method="post"> <fieldset class="step"> <img src="1.jpg" > </fieldset> <fieldset class="step"> <img src="2.jpg" > </fieldset> <fieldset class="step"> <img src="3.jpg" > </fieldset> </form> I tried doing something like: var imgSRC = $("div[id ='step']").get(1).find('img').attr('src'); alert(imgSRC); Got nothing....

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  • How to display in a form the next object of a collection?

    - by user359706
    I have a list of objects produced. after click on next I want to display the next product in the form my products list: Private List listProduct; listProduits = new List<Product>(); Product objProduit_1 = new Produit; objProduct_1.ref = "001"; objProduct_1.article = "G900"; objProduct_1.quantity = 30; listProducts.Add(objProduct_1); ProductobjProduit_2 = new Product; objProduct_2.ref = "002"; objProduct_2.article = "G900"; objProduct_2.quantity = 35; listProduits.Add(objProduct_2); in my asp page I have the following form: <form id="formNF" runat="server"> <asp:TextBox ID="txtRef" runat="server"></asp:TextBox> <asp:TextBox ID="txtArticle" runat="server"></asp:TextBox> <asp:TextBox ID="txtQauntity" runat="server"></asp:TextBox> <asp:Button ID="ButtonNext" runat="server" Text="Next product" OnClick="ButtonNext_Click"/> </form> In my code-behind: protected void ButtonNext_Click(object sender, EventArgs e) { // I do not know how to retrieve the following product // How to stop and continue after click on next button? foreach (Product prd in listProduct){ txtRef.Text = prd.ref; txtRef.Text = prd.article; txtRef.Text = prd.quantity; } } Thank you in advance.

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  • What's the right Java generic for a collection of elements with unique addressable indices?

    - by Rocreex
    I'm on my way to programming a database application and in our course we are told to implement a library of elements using one of the Java Collections. Each of the elements has a unique ID with which it's supposed to be addressed. Now I am wondering how this can be done. I though about using a ListArray but this won't work because the only way of addressing List elements is through the index which you can't control. Do you have some advice for me?

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  • How to query a collection of inherited object for a particular object type in grails ?

    - by quilovnic
    Hi, I have a this model : class Question{ Set components static hasMany = [components: QuestionComponent] } class QuestionComponent{ static belongsTo = Question } class QuestionComponentStatus extends QuestionComponent{ } class QuestionComponentOther extends QuestionComponent{ } I want to get only QuestionComponentStatus from Set components : questionInstance.components. ? Thanks a lot

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  • how to get value of button through jquery in formcollection with id of form collection?

    - by AbhijitPandya
    i have formcollection and two buttons like <form id="frmSubmitTax" method="post"> <input type="submit" id="btnTaxSave" value="Save" /> <input type="submit" id="btnTaxNext" value="Next" /> </form> i m submitting form through jquery and i want to get value of button while form submitting jquery code $('frmSubmitTax').live('submit', function (e) { get value of button that which button is submitted...... });

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  • C#/.NET &ndash; Finding an Item&rsquo;s Index in IEnumerable&lt;T&gt;

    - by James Michael Hare
    Sorry for the long blogging hiatus.  First it was, of course, the holidays hustle and bustle, then my brother and his wife gave birth to their son, so I’ve been away from my blogging for two weeks. Background: Finding an item’s index in List<T> is easy… Many times in our day to day programming activities, we want to find the index of an item in a collection.  Now, if we have a List<T> and we’re looking for the item itself this is trivial: 1: // assume have a list of ints: 2: var list = new List<int> { 1, 13, 42, 64, 121, 77, 5, 99, 132 }; 3:  4: // can find the exact item using IndexOf() 5: var pos = list.IndexOf(64); This will return the position of the item if it’s found, or –1 if not.  It’s easy to see how this works for primitive types where equality is well defined.  For complex types, however, it will attempt to compare them using EqualityComparer<T>.Default which, in a nutshell, relies on the object’s Equals() method. So what if we want to search for a condition instead of equality?  That’s also easy in a List<T> with the FindIndex() method: 1: // assume have a list of ints: 2: var list = new List<int> { 1, 13, 42, 64, 121, 77, 5, 99, 132 }; 3:  4: // finds index of first even number or -1 if not found. 5: var pos = list.FindIndex(i => i % 2 == 0);   Problem: Finding an item’s index in IEnumerable<T> is not so easy... This is all well and good for lists, but what if we want to do the same thing for IEnumerable<T>?  A collection of IEnumerable<T> has no indexing, so there’s no direct method to find an item’s index.  LINQ, as powerful as it is, gives us many tools to get us this information, but not in one step.  As with almost any problem involving collections, there are several ways to accomplish the same goal.  And once again as with almost any problem involving collections, the choice of the solution somewhat depends on the situation. So let’s look at a few possible alternatives.  I’m going to express each of these as extension methods for simplicity and consistency. Solution: The TakeWhile() and Count() combo One of the things you can do is to perform a TakeWhile() on the list as long as your find condition is not true, and then do a Count() of the items it took.  The only downside to this method is that if the item is not in the list, the index will be the full Count() of items, and not –1.  So if you don’t know the size of the list beforehand, this can be confusing. 1: // a collection of extra extension methods off IEnumerable<T> 2: public static class EnumerableExtensions 3: { 4: // Finds an item in the collection, similar to List<T>.FindIndex() 5: public static int FindIndex<T>(this IEnumerable<T> list, Predicate<T> finder) 6: { 7: // note if item not found, result is length and not -1! 8: return list.TakeWhile(i => !finder(i)).Count(); 9: } 10: } Personally, I don’t like switching the paradigm of not found away from –1, so this is one of my least favorites.  Solution: Select with index Many people don’t realize that there is an alternative form of the LINQ Select() method that will provide you an index of the item being selected: 1: list.Select( (item,index) => do something here with the item and/or index... ) This can come in handy, but must be treated with care.  This is because the index provided is only as pertains to the result of previous operations (if any).  For example: 1: // assume have a list of ints: 2: var list = new List<int> { 1, 13, 42, 64, 121, 77, 5, 99, 132 }; 3:  4: // you'd hope this would give you the indexes of the even numbers 5: // which would be 2, 3, 8, but in reality it gives you 0, 1, 2 6: list.Where(item => item % 2 == 0).Select((item,index) => index); The reason the example gives you the collection { 0, 1, 2 } is because the where clause passes over any items that are odd, and therefore only the even items are given to the select and only they are given indexes. Conversely, we can’t select the index and then test the item in a Where() clause, because then the Where() clause would be operating on the index and not the item! So, what we have to do is to select the item and index and put them together in an anonymous type.  It looks ugly, but it works: 1: // extensions defined on IEnumerable<T> 2: public static class EnumerableExtensions 3: { 4: // finds an item in a collection, similar to List<T>.FindIndex() 5: public static int FindIndex<T>(this IEnumerable<T> list, Predicate<T> finder) 6: { 7: // if you don't name the anonymous properties they are the variable names 8: return list.Select((item, index) => new { item, index }) 9: .Where(p => finder(p.item)) 10: .Select(p => p.index + 1) 11: .FirstOrDefault() - 1; 12: } 13: }     So let’s look at this, because i know it’s convoluted: First Select() joins the items and their indexes into an anonymous type. Where() filters that list to only the ones matching the predicate. Second Select() picks the index of the matches and adds 1 – this is to distinguish between not found and first item. FirstOrDefault() returns the first item found from the previous clauses or default (zero) if not found. Subtract one so that not found (zero) will be –1, and first item (one) will be zero. The bad thing is, this is ugly as hell and creates anonymous objects for each item tested until it finds the match.  This concerns me a bit but we’ll defer judgment until compare the relative performances below. Solution: Convert ToList() and use FindIndex() This solution is easy enough.  We know any IEnumerable<T> can be converted to List<T> using the LINQ extension method ToList(), so we can easily convert the collection to a list and then just use the FindIndex() method baked into List<T>. 1: // a collection of extension methods for IEnumerable<T> 2: public static class EnumerableExtensions 3: { 4: // find the index of an item in the collection similar to List<T>.FindIndex() 5: public static int FindIndex<T>(this IEnumerable<T> list, Predicate<T> finder) 6: { 7: return list.ToList().FindIndex(finder); 8: } 9: } This solution is simplicity itself!  It is very concise and elegant and you need not worry about anyone misinterpreting what it’s trying to do (as opposed to the more convoluted LINQ methods above). But the main thing I’m concerned about here is the performance hit to allocate the List<T> in the ToList() call, but once again we’ll explore that in a second. Solution: Roll your own FindIndex() for IEnumerable<T> Of course, you can always roll your own FindIndex() method for IEnumerable<T>.  It would be a very simple for loop which scans for the item and counts as it goes.  There’s many ways to do this, but one such way might look like: 1: // extension methods for IEnumerable<T> 2: public static class EnumerableExtensions 3: { 4: // Finds an item matching a predicate in the enumeration, much like List<T>.FindIndex() 5: public static int FindIndex<T>(this IEnumerable<T> list, Predicate<T> finder) 6: { 7: int index = 0; 8: foreach (var item in list) 9: { 10: if (finder(item)) 11: { 12: return index; 13: } 14:  15: index++; 16: } 17:  18: return -1; 19: } 20: } Well, it’s not quite simplicity, and those less familiar with LINQ may prefer it since it doesn’t include all of the lambdas and behind the scenes iterators that come with deferred execution.  But does having this long, blown out method really gain us much in performance? Comparison of Proposed Solutions So we’ve now seen four solutions, let’s analyze their collective performance.  I took each of the four methods described above and run them over 100,000 iterations of lists of size 10, 100, 1000, and 10000 and here’s the performance results.  Then I looked for targets at the begining of the list (best case), middle of the list (the average case) and not in the list (worst case as must scan all of the list). Each of the times below is the average time in milliseconds for one execution as computer over the 100,000 iterations: Searches Matching First Item (Best Case)   10 100 1000 10000 TakeWhile 0.0003 0.0003 0.0003 0.0003 Select 0.0005 0.0005 0.0005 0.0005 ToList 0.0002 0.0003 0.0013 0.0121 Manual 0.0001 0.0001 0.0001 0.0001   Searches Matching Middle Item (Average Case)   10 100 1000 10000 TakeWhile 0.0004 0.0020 0.0191 0.1889 Select 0.0008 0.0042 0.0387 0.3802 ToList 0.0002 0.0007 0.0057 0.0562 Manual 0.0002 0.0013 0.0129 0.1255   Searches Where Not Found (Worst Case)   10 100 1000 10000 TakeWhile 0.0006 0.0039 0.0381 0.3770 Select 0.0012 0.0081 0.0758 0.7583 ToList 0.0002 0.0012 0.0100 0.0996 Manual 0.0003 0.0026 0.0253 0.2514   Notice something interesting here, you’d think the “roll your own” loop would be the most efficient, but it only wins when the item is first (or very close to it) regardless of list size.  In almost all other cases though and in particular the average case and worst case, the ToList()/FindIndex() combo wins for performance, even though it is creating some temporary memory to hold the List<T>.  If you examine the algorithm, the reason why is most likely because once it’s in a ToList() form, internally FindIndex() scans the internal array which is much more efficient to iterate over.  Thus, it takes a one time performance hit (not including any GC impact) to create the List<T> but after that the performance is much better. Summary If you’re concerned about too many throw-away objects, you can always roll your own FindIndex() method, but for sheer simplicity and overall performance, using the ToList()/FindIndex() combo performs best on nearly all list sizes in the average and worst cases.    Technorati Tags: C#,.NET,Litte Wonders,BlackRabbitCoder,Software,LINQ,List

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  • Oracle Enterprise Manager 12c Integration With Oracle Enterprise Manager Ops Center 11g

    - by Scott Elvington
    In a blog entry earlier this year, we announced the availability of the Ops Center 11g plug-in for Enterprise Manager 12c. In this article I will walk you through the process of deploying the plug-in on your existing Enterprise Manager agents and show you some of the capabilities the plug-in provides. We'll also look at the integration from the Ops Center perspective. I will show you how to set up the connection to Enterprise Manager and give an overview of the information that is available. Installing and Configuring the Ops Center Plug-in The plug-in is available for download from the Self Update page (Setup ? Extensibility ? Self Update). The plug-in name is “Ops Center Infrastructure stack”. Once you have downloaded the plug-in you can navigate to the Plug-In management page (Setup ? Extensibility ? Plug-ins) to begin deployment. The plug-in must first be deployed on the Management Server. You will need to provide the repository password of the SYS user in order to deploy the plug-in to the Management Server. There are a few pre-requisites that need to be completed on the Ops Center side before the plug-in can be deployed and configured on the desired Enterprise Manager agents. Any servers, whether physical or virtual, for which you wish to see metrics and alerts need to be managed by Ops Center. This means that the Operating System needs to have an Ops Center management agent installed as a minimum. The plug-in can provide even more value when Ops Center is also managing the other “layers of the stack”, for example the service processor, the blade chassis or the XSCF of an M-Series server. The more information that Ops Center has about the stack, the more information that will be visible within Enterprise Manager via the plug-in. In order to access the information within Ops Center, the plug-in requires a user to connect as. This user does not require any particular Ops Center permissions or roles, it simply needs to exist. You can create a specific “EMPlugin” user within Ops Center or use an existing user. Oracle recommends creating a specific, non-privileged user account within Ops Center for this purpose. From the Ops Center Administration section, select Enterprise Controller, click the Users tab and finally click the Add User icon to create the desired user account. For the purpose of this article I have discovered and managed the OS and service processor of the server where my Enterprise Manager 12c installation is hosted. With the plug-in deployed to the Management Server and the setup done within Ops Center, we're now ready to deploy the plug-in to the agents and configure the targets to communicate with the Ops Center Enterprise Controller. From the Setup menu select Add Targets then Add Targets Manually. Select the bottom radio button “Add Targets Manually by Specifying Target Monitoring Properties”, select Infrastructure Stack from the Target Type dropdown and finally, select the Monitoring Agent where you wish to deploy the plug-in. Click the Add Manually.... button and fill in the details for the new target using the appropriate hostname for your Enterprise Controller and the user and password details for the plug-in access user. After the target has been added to the agent you will need to allow a few minutes for the initial data collection to complete. Once completed you can see the new target in the All Targets list. All metric collections are enabled by default except one. To enable Infrastructure Stack Alarms collection, navigate to the newly added target and then to Target ? Monitoring ? Metric and Collection Settings. There you can click the “Disabled” link under Collection Schedule to enable collection and set your desired collection frequency. By default, a Warning level alert in Ops Center will equate to a Warning level event in Enterprise Manager and a Critical alert will equate to a Critical event. This mapping can be altered in the Metric and Collection Settings also. The default incident rules in Enterprise Manager only create incidents from Critical events so keep this in mind in case you want to see incidents generated for Warning or Info level alerts from Ops Center. Also, because Enterprise Manager already monitors the OS through it's Host target type, the plug-in does not pull OS alerts from Ops Center so as to prevent duplication. In addition to alert propagation, the plug-in also provides data for several reports detailing the topology and configuration of the stack as well as any hardware sensor data that is available. These are available from the Information Publisher Reports. Navigate there from the Enterprise ? Reports menu or directly from the Infrastructure Stack target of interest. As an example, here is a sample of the Hardware Sensors report showing some of the available sensor data. The report can also be exported to a CSV file format if desired. Connecting Ops Center to Enterprise Manager Repository For an Enterprise Manager user, the plug-in provides a deeper visibility to the state of the infrastructure underlying the databases and middleware. On the Ops Center side, there is also a greater visibility to the targets running on the infrastructure. To set up the Ops Center data collection, just navigate to the Administration section and select the Grid Control link. Select the Configure/Connect action from the right-hand menu and complete the wizard forms to enable the connection to the Enterprise Manager repository and UI. Be sure to use the sysman account when configuring the database connection. Once the job completes and the initial data synchronization is done you will see new Target tabs on your OS assets. The new tab lists all the Enterprise Manager targets and any alerts, availability and performance data specific to the selected target. It is also possible to use the GoTo icon to launch the Enterprise Manager BUI in context of the specific target or alert to drill into more detail. Hopefully this brief overview of the integration between Enterprise Manager and Ops Center has provided a jumpstart to getting a more complete view of the full stack of your enterprise systems.

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  • Of C# Iterators and Performance

    - by James Michael Hare
    Some of you reading this will be wondering, "what is an iterator" and think I'm locked in the world of C++.  Nope, I'm talking C# iterators.  No, not enumerators, iterators.   So, for those of you who do not know what iterators are in C#, I will explain it in summary, and for those of you who know what iterators are but are curious of the performance impacts, I will explore that as well.   Iterators have been around for a bit now, and there are still a bunch of people who don't know what they are or what they do.  I don't know how many times at work I've had a code review on my code and have someone ask me, "what's that yield word do?"   Basically, this post came to me as I was writing some extension methods to extend IEnumerable<T> -- I'll post some of the fun ones in a later post.  Since I was filtering the resulting list down, I was using the standard C# iterator concept; but that got me wondering: what are the performance implications of using an iterator versus returning a new enumeration?   So, to begin, let's look at a couple of methods.  This is a new (albeit contrived) method called Every(...).  The goal of this method is to access and enumeration and return every nth item in the enumeration (including the first).  So Every(2) would return items 0, 2, 4, 6, etc.   Now, if you wanted to write this in the traditional way, you may come up with something like this:       public static IEnumerable<T> Every<T>(this IEnumerable<T> list, int interval)     {         List<T> newList = new List<T>();         int count = 0;           foreach (var i in list)         {             if ((count++ % interval) == 0)             {                 newList.Add(i);             }         }           return newList;     }     So basically this method takes any IEnumerable<T> and returns a new IEnumerable<T> that contains every nth item.  Pretty straight forward.   The problem?  Well, Every<T>(...) will construct a list containing every nth item whether or not you care.  What happens if you were searching this result for a certain item and find that item after five tries?  You would have generated the rest of the list for nothing.   Enter iterators.  This C# construct uses the yield keyword to effectively defer evaluation of the next item until it is asked for.  This can be very handy if the evaluation itself is expensive or if there's a fair chance you'll never want to fully evaluate a list.   We see this all the time in Linq, where many expressions are chained together to do complex processing on a list.  This would be very expensive if each of these expressions evaluated their entire possible result set on call.    Let's look at the same example function, this time using an iterator:       public static IEnumerable<T> Every<T>(this IEnumerable<T> list, int interval)     {         int count = 0;         foreach (var i in list)         {             if ((count++ % interval) == 0)             {                 yield return i;             }         }     }   Notice it does not create a new return value explicitly, the only evidence of a return is the "yield return" statement.  What this means is that when an item is requested from the enumeration, it will enter this method and evaluate until it either hits a yield return (in which case that item is returned) or until it exits the method or hits a yield break (in which case the iteration ends.   Behind the scenes, this is all done with a class that the CLR creates behind the scenes that keeps track of the state of the iteration, so that every time the next item is asked for, it finds that item and then updates the current position so it knows where to start at next time.   It doesn't seem like a big deal, does it?  But keep in mind the key point here: it only returns items as they are requested. Thus if there's a good chance you will only process a portion of the return list and/or if the evaluation of each item is expensive, an iterator may be of benefit.   This is especially true if you intend your methods to be chainable similar to the way Linq methods can be chained.    For example, perhaps you have a List<int> and you want to take every tenth one until you find one greater than 10.  We could write that as:       List<int> someList = new List<int>();         // fill list here         someList.Every(10).TakeWhile(i => i <= 10);     Now is the difference more apparent?  If we use the first form of Every that makes a copy of the list.  It's going to copy the entire list whether we will need those items or not, that can be costly!    With the iterator version, however, it will only take items from the list until it finds one that is > 10, at which point no further items in the list are evaluated.   So, sounds neat eh?  But what's the cost is what you're probably wondering.  So I ran some tests using the two forms of Every above on lists varying from 5 to 500,000 integers and tried various things.    Now, iteration isn't free.  If you are more likely than not to iterate the entire collection every time, iterator has some very slight overhead:   Copy vs Iterator on 100% of Collection (10,000 iterations) Collection Size Num Iterated Type Total ms 5 5 Copy 5 5 5 Iterator 5 50 50 Copy 28 50 50 Iterator 27 500 500 Copy 227 500 500 Iterator 247 5000 5000 Copy 2266 5000 5000 Iterator 2444 50,000 50,000 Copy 24,443 50,000 50,000 Iterator 24,719 500,000 500,000 Copy 250,024 500,000 500,000 Iterator 251,521   Notice that when iterating over the entire produced list, the times for the iterator are a little better for smaller lists, then getting just a slight bit worse for larger lists.  In reality, given the number of items and iterations, the result is near negligible, but just to show that iterators come at a price.  However, it should also be noted that the form of Every that returns a copy will have a left-over collection to garbage collect.   However, if we only partially evaluate less and less through the list, the savings start to show and make it well worth the overhead.  Let's look at what happens if you stop looking after 80% of the list:   Copy vs Iterator on 80% of Collection (10,000 iterations) Collection Size Num Iterated Type Total ms 5 4 Copy 5 5 4 Iterator 5 50 40 Copy 27 50 40 Iterator 23 500 400 Copy 215 500 400 Iterator 200 5000 4000 Copy 2099 5000 4000 Iterator 1962 50,000 40,000 Copy 22,385 50,000 40,000 Iterator 19,599 500,000 400,000 Copy 236,427 500,000 400,000 Iterator 196,010       Notice that the iterator form is now operating quite a bit faster.  But the savings really add up if you stop on average at 50% (which most searches would typically do):     Copy vs Iterator on 50% of Collection (10,000 iterations) Collection Size Num Iterated Type Total ms 5 2 Copy 5 5 2 Iterator 4 50 25 Copy 25 50 25 Iterator 16 500 250 Copy 188 500 250 Iterator 126 5000 2500 Copy 1854 5000 2500 Iterator 1226 50,000 25,000 Copy 19,839 50,000 25,000 Iterator 12,233 500,000 250,000 Copy 208,667 500,000 250,000 Iterator 122,336   Now we see that if we only expect to go on average 50% into the results, we tend to shave off around 40% of the time.  And this is only for one level deep.  If we are using this in a chain of query expressions it only adds to the savings.   So my recommendation?  If you have a resonable expectation that someone may only want to partially consume your enumerable result, I would always tend to favor an iterator.  The cost if they iterate the whole thing does not add much at all -- and if they consume only partially, you reap some really good performance gains.   Next time I'll discuss some of my favorite extensions I've created to make development life a little easier and maintainability a little better.

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