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• MySql - Get row number on select

  - by George

  Can I run a select statement and get the row number if the items are sorted? I have a table like this: mysql> describe orders; +-------------+---------------------+------+-----+---------+----------------+ | Field | Type | Null | Key | Default | Extra | +-------------+---------------------+------+-----+---------+----------------+ | orderID | bigint(20) unsigned | NO | PRI | NULL | auto_increment | | itemID | bigint(20) unsigned | NO | | NULL | | +-------------+---------------------+------+-----+---------+----------------+ I can then run this query to get the number of orders by ID: SELECT itemID, COUNT(*) as ordercount FROM orders GROUP BY itemID ORDER BY ordercount DESC; This gives me a count of each itemID in the table like this: +--------+------------+ | itemID | ordercount | +--------+------------+ | 388 | 3 | | 234 | 2 | | 3432 | 1 | | 693 | 1 | | 3459 | 1 | +--------+------------+ I want to get the row number as well, so I could tell that itemID 388 is the first row, 234 is second, etc (essentially the ranking of the orders, not just a raw count). I know I can do this in java when I get the result set back, but I was wondering if there was a way to handle it purely in SQL.

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• Configuring Team City internal.properties to increase git fetch memory

  - by 78lro

  When pulling from GIT my Team City install is getting an out of memory error. According to the Team City documentation I should be able to increase the memory assigned to the git fetch process, by setting the value for teamcity.git.fetch.process.max.memory to something greater than the default 512MB. http://confluence.jetbrains.net/display/TCD65/Git+%28JetBrains%29#Git%28JetBrains%29-InternalProperties Problem is there does not appear to be an internal.properties file in the location specified. I have tried creating one in the TeamCity/conf/internal.properties as suggested here: http://devnet.jetbrains.net/thread/302596 But I still get the out of memory issue when Team City tries to pull from github thx

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• Proper usage of JTidy to purify HTML

  - by Raj

  Hello, I am trying to use JTidy (jtidy-r938.jar) to sanitize an input HTML string, but I seem to have problems getting the default settings right. Often strings such as "hello world" end up as "helloworld" after tidying. I wanted to show what I'm doing here, and any pointers would be really appreciated: Assume that rawHtml is the String containing the input (real world) HTML. This is what I'm doing: InputStream is = new ByteArrayInputStream(rawHtml.getBytes("UTF-8")); Tidy tidy = new Tidy(); tidy.setQuiet(true); tidy.setShowWarnings(false); tidy.setXHTML(true); ByteArrayOutputStream baos = new ByteArrayOutputStream(); tidy.parseDOM(is, baos); String pure = baos.toString(); First off, does anything look fundamentally wrong with the above code? I seem to be getting weird results with this. Thanks in advance!

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• JMeter to grab full querystring into a variable for future use

  - by jfbauer

  Someone provided me the regex to parse out a query string: (?<=\?)[^?]+$ I am trying to use that in JMeter with no luck (although I am successful in pulling out individual query string parameter values based on various example postings on the web). I created a regular expression extractor called "Grab QueryString". I selected the URL response field to check. For the reference name, I typed "myQueryString". For the regular expression, I entered your text. For template, I entered $1$ Match no = 1 Default Value = ERROR Unfortunately, "myQueryString" is getting populated with ERROR and not the URL query string as hoped when I try and use it as a parameter in a future GET. Thus, I see this in the "View Results Tree": https:/www.website.com/folder/page.aspx?ERROR Instead of: https:/www.website.com/folder/page.aspx?jfhjHSDjgdjhsjhsdhjSJHWed Did I do something wrong? Anyone have any suggestions?

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• How should I use this SetSPN command when installing SharePoint

  - by Paul Rowland

  In the SharePoint install document I have it says, If you use a domain user account for the SQL Server service account, you must make sure that a valid service principal name (SPN) for that account and instance of SQL Server on their database server exists in their environment. This is the case regardless of whether you use NTLM or Kerberos authentication for Office SharePoint Server 2007. You must configure the SPN for that account in the domain using the Setspn.exe command-line tool. Setspn.exe is installed by default on computers running Windows Server 2008. Run the following command on a computer that is joined to the same domain as the user/service account. setspn -a <http/<farmclusterdnsname> <serviceaccountname> What should the parameters be in this case? I guess the serviceaccountname would be 'domain\username' not sure what the first parameter should be though. This is the technet link for SetSPN.

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• wix: does INSTALLDIR always end in a slash?

  - by Cheeso

  I think the default dir gets a trailing slash. But what if the user selects a different directory? Is there a way for the INSTALLDIR to NOT have a trailing slash? It's not that I want it to not have a trailing slash. I want to know if I can count on it, so that, for example, [INSTALLDIR]Filter.dll ...will always resolve to a real, valid filesystem path. Currently I use [INSTALLDIR]\Filter.dll and I get a double-slash in there. It's valid and resolves, but I'd like to eliminate the double slash. thanks.

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• Installing JBoss Drools Eclipse IDE Plugin: JUnit dependency. How do I install it?

  - by ?????

  I'm new to this whole JBoss/JUnit world. I'm trying to install the JBoss Drools plugin for the Eclipse IDE and I get this error. Cannot complete the install because one or more required items could not be found. Software currently installed: JBoss Drools Core 5.0.1 (org.drools.eclipse.feature.feature.group 5.0.1) Missing requirement: Drools Eclipse Plug-in 5.0.1 (org.drools.eclipse 5.0.1) requires 'bundle org.eclipse.jdt.junit 0.0.0' but it could not be found Cannot satisfy dependency: From: JBoss Drools Core 5.0.1 (org.drools.eclipse.feature.feature.group 5.0.1) To: org.drools.eclipse [5.0.1] I downloaded junit and told Eclipse to add it to the default classpath, and also added it to my login CLASSPATH variable, but Eclipse still complains. What's the proper way to install the plugin?

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• Optimizations employed by ORM's

  - by Kartoch

  I'm teaching JEE, especially JPA, Spring and Spring MVC. As I have not so much experience in large projects, it is difficult to know what to present to students about optimisation of ORM. At the present time, I present some classic optimisation tricks: prepared statements (most of ORM implicitely uses it by default) first and second-level caches "write first, optimize later" it is possible to switch off ORM and send SQL commands directly to the database for very frequent, specialized and costly requests Is there any other point the community see about other way to optimize ORM ? I'm especially interested by DAO patterns...

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• Handle "Cannot access a closed resource set"

  - by Philip

  I have a website with several languages in a database. From the database I use ResXResourceWriter to create my .resx files. This is working really good but sometimes I get this exception: MESSAGE: Cannot access a closed resource set. SOURCE: mscorlib FORM: QUERYSTRING: TARGETSITE: System.Object GetObject(System.String, Boolean, Boolean) STACKTRACE: at System.Resources.RuntimeResourceSet.GetObject(String key, Boolean ignoreCase, Boolean isString) at System.Resources.RuntimeResourceSet.GetString(String key, Boolean ignoreCase) at System.Resources.ResourceManager.GetString(String name, CultureInfo culture) at System.Linq.Expressions.Expression.ValidateStaticOrInstanceMethod(Expression instance, MethodInfo method) at System.Linq.Expressions.Expression.Call(Expression instance, MethodInfo method, IEnumerable`1 arguments) at System.Data.Linq.DataContext.GetMethodCall(Object instance, MethodInfo methodInfo, Object[] parameters) at System.Data.Linq.DataContext.ExecuteMethodCall(Object instance, MethodInfo methodInfo, Object[] parameters) at Business.DatabaseModelDataContext.Web_GetMostPlayedEvents(String cultureCode) at Presentation.Default.Page_Load(Object sender, EventArgs e) at System.Web.Util.CalliHelper.EventArgFunctionCaller(IntPtr fp, Object o, Object t, EventArgs e) at System.Web.UI.Control.LoadRecursive() at System.Web.UI.Page.ProcessRequestMain(Boolean includeStagesBeforeAsyncPoint, Boolean includeStagesAfterAsyncPoint) I don't know why this is happening or how to solve it. Does anyone know anything about this? Thanks, Philip

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• Loading Magento child html outside of Magento

  - by Christian Thamer

  I am loading Magento blocks outside of Magento for certain parts of my site. I can do this successfully with something similar the following. require_once $docRoot.'/app/Mage.php'; umask(0); Mage::app('default'); ... $layout = Mage::getSingleton('core/layout'); $block = $layout->createBlock('Mage_Page_Block_Html_Header'); $block->setTemplate('page/html/header.phtml'); echo $block->renderView(); The problem is that if the block I am rending has child blocks(html) they are not included in the output. In the example above the file header.phtml contains the following call for child html that is missing from the output. ... <?php echo $this->getChildHtml('topLinks') ?> ...

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• Freemarker/Velocity - date manipulation

  - by Razor

  Hello, I have a fairly simple question about these 2 templating engines. I'm trying to make a future/paste date, a fixed time from now, e.g. 18 months ago, or tomorrow. I know that it is possible to do this with a java date object inside a velocity/freemarker template (something like $date.add(2,-18)), but I would like to do this with DateTool or freemarker core. This is something that I see as purely presentational (just think at the default dates you see in flight booking forms), so I can't see any reason why a templating engine shouldn't be able to do this. Is it possible though? If so, how?

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• High-quality ERD generator for PostgresQL under Linux?

  - by Dave Jarvis

  Background MySQL Workbench can produce appealing and high-quality ERDs such as: Research I have not found a tool that even comes close for PostgreSQL. Tools I have found: dbVisualizer - Yellow squares. AquaFold - Yellow squares. SQL Developer - Coloured squares. Dia - Coloured squares. SchemaBank - Can't export to PNG; looks okay, nothing stellar. SchemaSpy - XML export makes it possible to write an XSL skin... Gliffy - Incompatible Flash version. Druid - No. pgAdmin3 - Not applicable? phpPgAdmin - Couldn't login without a 30-minute configuration battle. Requirements Looking for an ERD tool: Visually stunning by default Can reverse-engineer a PostgreSQL (or JDBC-compliant) database Runs on Linux (or under WINE) Export high-resolution PNG (or SVG) FOSS

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• UITableView insertRowsAtIndexPaths out of order

  - by bschlenk

  I currently have a UISegmentedControl set to add/remove table view cells when its value changes. Removing cells works perfectly, however when I insert cells they're in reverse order every other time. NSArray *addindexes = [NSArray arrayWithObjects:[NSIndexPath indexPathForRow:2 inSection:0], [NSIndexPath indexPathForRow:3 inSection:0], [NSIndexPath indexPathForRow:4 inSection:0], nil]; NSArray *removeindexes = [NSArray arrayWithObjects:[NSIndexPath indexPathForRow:2 inSection:0], [NSIndexPath indexPathForRow:3 inSection:0], [NSIndexPath indexPathForRow:4 inSection:0], nil]; [self.tableView beginUpdates]; switch (switchType.selectedSegmentIndex) { case 0: [self.tableView insertRowsAtIndexPaths:addindexes withRowAnimation:UITableViewRowAnimationTop]; break; case 1: [self.tableView deleteRowsAtIndexPaths:removeindexes withRowAnimation:UITableViewRowAnimationTop]; break; default: break; } [self.tableView endUpdates];} For example, every other time I add/remove cells they're in reverse order. (4, 3, 2 instead of 2, 3, 4) 1) Remove cells- add cells- correct order 2) Remove cells- add cells- incorrect order 3) Remove cells- add cells- correct order

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• SSRS 2008 - How to hide the plus icon in a group visibility toggle cell

  - by Daniel Coffman

  I have a report that shows or hides columns in a group based on a header cell. SSRS makes this pretty easy and is kind enough to place a little plus/minus icon in the toggling cell. I want to HIDE this plus/minus icon when there is only one column of data in the subgroup, because it shows that one column by default so expanding the group doesn't do anything. This really only applies to one specific group, because all the others always have more than one column of data, so a way to hide only the icon for a specific group would be fine. JavaScript won't work (I don't think) because the client ID of the plus/minus image is generated by the report and changes with each generation. see this image for more clarity: http://imgur.com/vqaQA.png

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• Is is possible to enable persistent cookies and disable session cookies?

  - by Sem Dendoncker

  Hello, We have an application that uses a persistent cookie to store the language of the user and a session cookie for authentication. Now our site starts with a number of tests such as: javascript, cookies, flash plugin, sound and popup and only if all tests succeed you can go to the logon page. After logging in you can see the application. Now one of our clients has a serieus problem, she passes all the tests but upon logging in she goes to the default page and get's redirected tot the logon page again. (form authentication). Now I was wondering how this is possible. It's allmost like a persistent cookie is enabled (otherweise she's not able to skip the language page) and a session cookie isn't. I hope this explains it a bit. Cheers, M.

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• How can I set the Inital Orientation for a UISplitViewCOntroller-based iPad App

  - by MystikSpiral

  I have a split view app running fine on the iPad. It is using the default setup (Popover in Portrait, table view on the left in landscape). The views shift correctly once the app is running. The problem I am seeing is that when the app starts (in the simulator) running in landscape mode the UI paradigm is the one intended for Portrait mode (Master List is a popover) is what loads. I am thinking this is some strangeness with the simulator, or I am missing an option on my main view controller.

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• Force "Internet Explorer 8" browser mode in intranet

  - by Dennis Cheung

  There are "Internet Explorer 8", "Internet Explorer 8 Compatibility Mode", and IE7 mode in IE8. However, the default setting in IE make all intranet website use "IE8 Compatibility Mode" even I have setted doctype, the meta tag, http header as suggested to force it into IE8 mode. I have <!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd" and <meta http-equiv="X-UA-Compatible" content="IE=8" But it still goes into "IE8 Compatibility Mode", without any changes in IE setting. How to force it into pure "IE8" mode, without change any browser's setting? PS. I am not talking "document mode" here.

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• PostSharp OnMethodBoundaryAspect

  - by José F. Romaniello

  I'm working on an aspect with postsharp 1.5 and OnMethodBoundaryAspect. I want my aspect have the following behavior by default: 1-If the attribute is used at class level the aspect is applied only on PUBLIC methods. 2-The user of the aspect can put the aspect in a private or protected method. If I use this [MulticastAttributeUsage( MulticastTargets.Method, TargetMemberAttributes = MulticastAttributes.Public)] the point 1 works, but the case 2 doesn't even build becaue is incompatible. Then I tried to use: AttributeTargetTypeAttributes = MulticastAttributes.Public; in the constructor of the aspect, but doesn't work. Thank you very much in advance.

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• Hide ticks at Min and Max in WPF Slider

  - by gehho

  Hi, I want to display a Slider ranging from 0.5 to 1.5 with only one tick mark at 1.0 to mark the center and default value. I have defined a Slider as follows: <Slider Minimum="0.5" Maximum="1.5" IsMoveToPointEnabled="True" IsSnapToTickEnabled="False" Orientation="Horizontal" Ticks="1.0" TickPlacement="BottomRight" Value="{Binding SomeProperty, Mode=TwoWay}"/> However, besides a tick mark at 0.0 this Slider also shows tick marks at 0.5 and 1.5, i.e. the Minimum and Maximum values. Is there a way to hide these min/max tick marks?! I checked all properties and tried changing some of them, but did not have success so far. Thanks, gehho.

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• Tree View / File View Control for C#

  - by Jason

  I have been looking for a C# tree control for displaying a file system that has the following capabilities: Select a starting directory. I don't always want to start at a "default" top directory level. The ability to grab an event when the user double clicks on a file in the tree. I want to handle opening the file within my application. I have been looking at this C# File Browser. Unfortunately, I have not been able to figure out how to do meet my second need. (If anybody can clear that up for me, I would like that even better.) Thanks for any help.

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• install SSMSE 2008 after VS 2010

  - by snehalpatkar

  hi guys i have installed VS 2010 ultimate on windows 7 machine which by default install sql server 2008. now i want to install SSMSE 2008 i download the following file SQLEXPRWT_x86_ENU and tried to install it but it give me error. [Window Title] Program Compatibility Assistant [Main Instruction] This program has known compatibility issues [Expanded Information] After SQL Server Setup completes, you must apply SQL Server 2008 Service Pack 1 (SP1) or a later service pack before you run SQL Server 2008 on this version of Windows. [^] Hide details [ ] Don't show this message again [Check for solutions online] [Run program] [Cancel] TITLE: SQL Server Setup failure. SQL Server Setup has encountered the following error: Invoke or BeginInvoke cannot be called on a control until the window handle has been created.. BUTTONS: OK how to install SSMSE 2008 after installing VS 2010 please help

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• How to send mail from ASP.NET with IIS6 SMTP in a dedicated server?

  - by Julio César

  Hi. I'm trying to configure a dedicated server that runs ASP.NET to send mail through the local IIS SMTP server but mail is getting stuck in the Queue folder and doesn't get delivered. I'm using this code in an .aspx page to test: <%@ Page Language="C#" AutoEventWireup="true" %> <% new System.Net.Mail.SmtpClient("localhost").Send("[email protected]", "[email protected]", "testing...", "Hello, world.com"); %> Then, I added the following to the Web.config file: <system.net> <mailSettings> <smtp> <network host="localhost"/> </smtp> </mailSettings> </system.net> In the IIS Manager I've changed the following in the properties of the "Default SMTP Virtual Server". General: [X] Enable Logging Access / Authentication: [X] Windows Integrated Authentication Access / Relay Restrictions: (o) Only the list below, Granted 127.0.0.1 Delivery / Advanced: Fully qualified domain name = thedomain.com Finally, I run the SMTPDiag.exe tool like this: C:\>smtpdiag.exe [email protected] [email protected] Searching for Exchange external DNS settings. Computer name is THEDOMAIN. Failed to connect to the domain controller. Error: 8007054b Checking SOA for gmail.com. Checking external DNS servers. Checking internal DNS servers. SOA serial number match: Passed. Checking local domain records. Checking MX records using TCP: thedomain.com. Checking MX records using UDP: thedomain.com. Both TCP and UDP queries succeeded. Local DNS test passed. Checking remote domain records. Checking MX records using TCP: gmail.com. Checking MX records using UDP: gmail.com. Both TCP and UDP queries succeeded. Remote DNS test passed. Checking MX servers listed for [email protected]. Connecting to gmail-smtp-in.l.google.com [209.85.199.27] on port 25. Connecting to the server failed. Error: 10060 Failed to submit mail to gmail-smtp-in.l.google.com. Connecting to gmail-smtp-in.l.google.com [209.85.199.114] on port 25. Connecting to the server failed. Error: 10060 Failed to submit mail to gmail-smtp-in.l.google.com. Connecting to alt2.gmail-smtp-in.l.google.com [209.85.135.27] on port 25. Connecting to the server failed. Error: 10060 Failed to submit mail to alt2.gmail-smtp-in.l.google.com. Connecting to alt2.gmail-smtp-in.l.google.com [209.85.135.114] on port 25. Connecting to the server failed. Error: 10060 Failed to submit mail to alt2.gmail-smtp-in.l.google.com. Connecting to alt1.gmail-smtp-in.l.google.com [209.85.133.27] on port 25. Connecting to the server failed. Error: 10060 Failed to submit mail to alt1.gmail-smtp-in.l.google.com. Connecting to alt2.gmail-smtp-in.l.google.com [74.125.79.27] on port 25. Connecting to the server failed. Error: 10060 Failed to submit mail to alt2.gmail-smtp-in.l.google.com. Connecting to alt2.gmail-smtp-in.l.google.com [74.125.79.114] on port 25. Connecting to the server failed. Error: 10060 Failed to submit mail to alt2.gmail-smtp-in.l.google.com. Connecting to alt1.gmail-smtp-in.l.google.com [209.85.133.114] on port 25. Connecting to the server failed. Error: 10060 Failed to submit mail to alt1.gmail-smtp-in.l.google.com. Connecting to gsmtp183.google.com [64.233.183.27] on port 25. Connecting to the server failed. Error: 10060 Failed to submit mail to gsmtp183.google.com. Connecting to gsmtp147.google.com [209.85.147.27] on port 25. Connecting to the server failed. Error: 10051 Failed to submit mail to gsmtp147.google.com. I'm using ASP.NET 2.0, Windows 2003 Server and the IIS that comes with it. Can you tell me what else to change to fix the problem? Thanks @mattlant This is a dedicated server that's why I'm installing the SMTP manually. EDIT: I use exchange so its a little different, but its called a smart host in exchange, but in plain SMTP service config i think its called something else. Cant remember exactly the setting name. Thank you for pointing me at the Smart host field. Mail is getting delivered now. In the Default SMTP Virtual Server properties, the Delivery tab, click Advanced and fill the "Smart host" field with the address that your provider gives you. In my case (GoDaddy) it was k2smtpout.secureserver.net. More info here: http://help.godaddy.com/article/1283

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• Getting ActiveRecord (Rails) to_xml to use xsi:nil and xsi:type instead of nil and type

  - by nbeyer

  The default behavior of XML serialization (to_xml) for ActiveRecord objects will emit 'type' and 'nil' attributes that are similar to XML Schema Instance attributes, but aren't set in a XML Namespace. For example, a model might produce an output like this: <user> <username nil="true" /> <first-name type="string">Name</first-name> </user> Is there anyway to get to_xml to utilize the XML Schema Instance namespace and prefix the attributes and the values? Using the above example, I'd like to produce the following: <user xmlns:xsi="http://www.w3.org/1999/XMLSchema-instance" xmlns:xs="http://www.w3.org/1999/XMLSchema"> <username xsi:nil="true" /> <first-name xsi:type="xs:string">Name</first-name> </user>

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• Does jQuery ajaxSetup({cache: true}) generally work?

  - by fsb

  jQuery 1.4.2 omits the timestamp GET parameter (to defeat browser cacheing) if I assert the ajax cache setting in the local context: $.ajax({ url: searcher, data: keys, cache: true, type: 'GET', dataType: 'json', success: function(data) { // something }); But it includes timestamp if I move the setting out of there and into the global context: $.ajaxSetup({cache: true}); Moreover, if I let the default apply, jQuery sets timestamp, which doesn't seem to match the manual. Do you experience the same? Do HTTP cache control response headers from the server affect this jQuery feature?

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• Sorting Algorithms

  - by MarkPearl

  General Every time I go back to university I find myself wading through sorting algorithms and their implementation in C++. Up to now I haven’t really appreciated their true value. However as I discovered this last week with Dictionaries in C# – having a knowledge of some basic programming principles can greatly improve the performance of a system and make one think twice about how to tackle a problem. I’m going to cover briefly in this post the following: Selection Sort Insertion Sort Shellsort Quicksort Mergesort Heapsort (not complete) Selection Sort Array based selection sort is a simple approach to sorting an unsorted array. Simply put, it repeats two basic steps to achieve a sorted collection. It starts with a collection of data and repeatedly parses it, each time sorting out one element and reducing the size of the next iteration of parsed data by one. So the first iteration would go something like this… Go through the entire array of data and find the lowest value Place the value at the front of the array The second iteration would go something like this… Go through the array from position two (position one has already been sorted with the smallest value) and find the next lowest value in the array. Place the value at the second position in the array This process would be completed until the entire array had been sorted. A positive about selection sort is that it does not make many item movements. In fact, in a worst case scenario every items is only moved once. Selection sort is however a comparison intensive sort. If you had 10 items in a collection, just to parse the collection you would have 10+9+8+7+6+5+4+3+2=54 comparisons to sort regardless of how sorted the collection was to start with. If you think about it, if you applied selection sort to a collection already sorted, you would still perform relatively the same number of iterations as if it was not sorted at all. Many of the following algorithms try and reduce the number of comparisons if the list is already sorted – leaving one with a best case and worst case scenario for comparisons. Likewise different approaches have different levels of item movement. Depending on what is more expensive, one may give priority to one approach compared to another based on what is more expensive, a comparison or a item move. Insertion Sort Insertion sort tries to reduce the number of key comparisons it performs compared to selection sort by not “doing anything” if things are sorted. Assume you had an collection of numbers in the following order… 10 18 25 30 23 17 45 35 There are 8 elements in the list. If we were to start at the front of the list – 10 18 25 & 30 are already sorted. Element 5 (23) however is smaller than element 4 (30) and so needs to be repositioned. We do this by copying the value at element 5 to a temporary holder, and then begin shifting the elements before it up one. So… Element 5 would be copied to a temporary holder 10 18 25 30 23 17 45 35 – T 23 Element 4 would shift to Element 5 10 18 25 30 30 17 45 35 – T 23 Element 3 would shift to Element 4 10 18 25 25 30 17 45 35 – T 23 Element 2 (18) is smaller than the temporary holder so we put the temporary holder value into Element 3. 10 18 23 25 30 17 45 35 – T 23   We now have a sorted list up to element 6. And so we would repeat the same process by moving element 6 to a temporary value and then shifting everything up by one from element 2 to element 5. As you can see, one major setback for this technique is the shifting values up one – this is because up to now we have been considering the collection to be an array. If however the collection was a linked list, we would not need to shift values up, but merely remove the link from the unsorted value and “reinsert” it in a sorted position. Which would reduce the number of transactions performed on the collection. So.. Insertion sort seems to perform better than selection sort – however an implementation is slightly more complicated. This is typical with most sorting algorithms – generally, greater performance leads to greater complexity. Also, insertion sort performs better if a collection of data is already sorted. If for instance you were handed a sorted collection of size n, then only n number of comparisons would need to be performed to verify that it is sorted. It’s important to note that insertion sort (array based) performs a number item moves – every time an item is “out of place” several items before it get shifted up. Shellsort – Diminishing Increment Sort So up to now we have covered Selection Sort & Insertion Sort. Selection Sort makes many comparisons and insertion sort (with an array) has the potential of making many item movements. Shellsort is an approach that takes the normal insertion sort and tries to reduce the number of item movements. In Shellsort, elements in a collection are viewed as sub-collections of a particular size. Each sub-collection is sorted so that the elements that are far apart move closer to their final position. Suppose we had a collection of 15 elements… 10 20 15 45 36 48 7 60 18 50 2 19 43 30 55 First we may view the collection as 7 sub-collections and sort each sublist, lets say at intervals of 7 10 60 55 – 20 18 – 15 50 – 45 2 – 36 19 – 48 43 – 7 30 10 55 60 – 18 20 – 15 50 – 2 45 – 19 36 – 43 48 – 7 30 (Sorted) We then sort each sublist at a smaller inter – lets say 4 10 55 60 18 – 20 15 50 2 – 45 19 36 43 – 48 7 30 10 18 55 60 – 2 15 20 50 – 19 36 43 45 – 7 30 48 (Sorted) We then sort elements at a distance of 1 (i.e. we apply a normal insertion sort) 10 18 55 60 2 15 20 50 19 36 43 45 7 30 48 2 7 10 15 18 19 20 30 36 43 45 48 50 55 (Sorted) The important thing with shellsort is deciding on the increment sequence of each sub-collection. From what I can tell, there isn’t any definitive method and depending on the order of your elements, different increment sequences may perform better than others. There are however certain increment sequences that you may want to avoid. An even based increment sequence (e.g. 2 4 8 16 32 …) should typically be avoided because it does not allow for even elements to be compared with odd elements until the final sort phase – which in a way would negate many of the benefits of using sub-collections. The performance on the number of comparisons and item movements of Shellsort is hard to determine, however it is considered to be considerably better than the normal insertion sort. Quicksort Quicksort uses a divide and conquer approach to sort a collection of items. The collection is divided into two sub-collections – and the two sub-collections are sorted and combined into one list in such a way that the combined list is sorted. The algorithm is in general pseudo code below… Divide the collection into two sub-collections Quicksort the lower sub-collection Quicksort the upper sub-collection Combine the lower & upper sub-collection together As hinted at above, quicksort uses recursion in its implementation. The real trick with quicksort is to get the lower and upper sub-collections to be of equal size. The size of a sub-collection is determined by what value the pivot is. Once a pivot is determined, one would partition to sub-collections and then repeat the process on each sub collection until you reach the base case. With quicksort, the work is done when dividing the sub-collections into lower & upper collections. The actual combining of the lower & upper sub-collections at the end is relatively simple since every element in the lower sub-collection is smaller than the smallest element in the upper sub-collection. Mergesort With quicksort, the average-case complexity was O(nlog2n) however the worst case complexity was still O(N*N). Mergesort improves on quicksort by always having a complexity of O(nlog2n) regardless of the best or worst case. So how does it do this? Mergesort makes use of the divide and conquer approach to partition a collection into two sub-collections. It then sorts each sub-collection and combines the sorted sub-collections into one sorted collection. The general algorithm for mergesort is as follows… Divide the collection into two sub-collections Mergesort the first sub-collection Mergesort the second sub-collection Merge the first sub-collection and the second sub-collection As you can see.. it still pretty much looks like quicksort – so lets see where it differs… Firstly, mergesort differs from quicksort in how it partitions the sub-collections. Instead of having a pivot – merge sort partitions each sub-collection based on size so that the first and second sub-collection of relatively the same size. This dividing keeps getting repeated until the sub-collections are the size of a single element. If a sub-collection is one element in size – it is now sorted! So the trick is how do we put all these sub-collections together so that they maintain their sorted order. Sorted sub-collections are merged into a sorted collection by comparing the elements of the sub-collection and then adjusting the sorted collection. Lets have a look at a few examples… Assume 2 sub-collections with 1 element each 10 & 20 Compare the first element of the first sub-collection with the first element of the second sub-collection. Take the smallest of the two and place it as the first element in the sorted collection. In this scenario 10 is smaller than 20 so 10 is taken from sub-collection 1 leaving that sub-collection empty, which means by default the next smallest element is in sub-collection 2 (20). So the sorted collection would be 10 20 Lets assume 2 sub-collections with 2 elements each 10 20 & 15 19 So… again we would Compare 10 with 15 – 10 is the winner so we add it to our sorted collection (10) leaving us with 20 & 15 19 Compare 20 with 15 – 15 is the winner so we add it to our sorted collection (10 15) leaving us with 20 & 19 Compare 20 with 19 – 19 is the winner so we add it to our sorted collection (10 15 19) leaving us with 20 & _ 20 is by default the winner so our sorted collection is 10 15 19 20. Make sense? Heapsort (still needs to be completed) So by now I am tired of sorting algorithms and trying to remember why they were so important. I think every year I go through this stuff I wonder to myself why are we made to learn about selection sort and insertion sort if they are so bad – why didn’t we just skip to Mergesort & Quicksort. I guess the only explanation I have for this is that sometimes you learn things so that you can implement them in future – and other times you learn things so that you know it isn’t the best way of implementing things and that you don’t need to implement it in future. Anyhow… luckily this is going to be the last one of my sorts for today. The first step in heapsort is to convert a collection of data into a heap. After the data is converted into a heap, sorting begins… So what is the definition of a heap? If we have to convert a collection of data into a heap, how do we know when it is a heap and when it is not? The definition of a heap is as follows: A heap is a list in which each element contains a key, such that the key in the element at position k in the list is at least as large as the key in the element at position 2k +1 (if it exists) and 2k + 2 (if it exists). Does that make sense? At first glance I’m thinking what the heck??? But then after re-reading my notes I see that we are doing something different – up to now we have really looked at data as an array or sequential collection of data that we need to sort – a heap represents data in a slightly different way – although the data is stored in a sequential collection, for a sequential collection of data to be in a valid heap – it is “semi sorted”. Let me try and explain a bit further with an example… Example 1 of Potential Heap Data Assume we had a collection of numbers as follows 1[1] 2[2] 3[3] 4[4] 5[5] 6[6] For this to be a valid heap element with value of 1 at position [1] needs to be greater or equal to the element at position [3] (2k +1) and position [4] (2k +2). So in the above example, the collection of numbers is not in a valid heap. Example 2 of Potential Heap Data Lets look at another collection of numbers as follows 6[1] 5[2] 4[3] 3[4] 2[5] 1[6] Is this a valid heap? Well… element with the value 6 at position 1 must be greater or equal to the element at position [3] and position [4]. Is 6 > 4 and 6 > 3? Yes it is. Lets look at element 5 as position 2. It must be greater than the values at [4] & [5]. Is 5 > 3 and 5 > 2? Yes it is. If you continued to examine this second collection of data you would find that it is in a valid heap based on the definition of a heap.

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