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  • In SICP exercise 2.26 using DrScheme, why does cons return a list, instead of a pair of lists?

    - by limist
    In SICP exercise 2.26, this Scheme code is given: (define x (list 1 2 3)) (define y (list 4 5 6)) Then this cons call is given: (cons x y) I expected a pair of lists would result, ((1 2 3) (4 5 6)) but the interpreter gives, ((1 2 3) 4 5 6) ...a list with 4 elements, the first being a list. Why is y treated differently? I've tried looking up other SICP answers for an explanation, but couldn't find something satisfactory. So could any Scheme/Lisp experts please shed some light on this aspect of cons? Thanks in advance for any insight.

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  • How do I get Mathematica to thread a 2-variable function over two lists, using functional programmin

    - by Leah Wrenn Berman
    Lets say I have a function f[x_, y_], and two lists l1, l2. I'd like to evaluate f[x,y] where x runs over the list l1 and y runs over the list l2, and I'd like to do it without having to make all pairs of the form {l1[[i]],l2[[j]]}. (Motivation: I'm trying to implement some basic Haskell programs in Mathematica. In particular, I'd like to be able to code the Haskell program isMatroid::[[Int]]->Bool isMatroid b =and[or[sort(union(xs\\[x])[y]'elem'b|y<-ys]|xs<-b,ys<-b, xs<-x] I think I can do the rest of it, if I can figure out the original question, but I'd like the code to be Haskell-like. Any suggestions for implementing Haskell-like code in Mathematica would be appreciated.)

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  • Why are difference lists more efficient than regular concatenation?

    - by Craig Innes
    I am currently working my way through the Learn you a haskell book online, and have come to a chapter where the author is explaining that some list concatenations can be ineffiecient: For example ((((a ++ b) ++ c) ++ d) ++ e) ++ f Is supposedly inefficient. The solution the author comes up with is to use 'difference lists' defined as newtype DiffList a = DiffList {getDiffList :: [a] -> [a] } instance Monoid (DiffList a) where mempty = DiffList (\xs -> [] ++ xs) (DiffList f) `mappend` (DiffList g) = DiffList (\xs -> f (g xs)) I am struggling to understand why DiffList is more computationally efficient than a simple concatenation in some cases. Could someone explain to me in simple terms why the above example is so inefficient, and in what way the DiffList solves this problem?

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  • Can anyone help with java? Finding common nodes from two linked lists using recursion

    - by Dan
    I have to write a method that returns a linked list with all the nodes that are common to two linked lists using recursion, without loops. For example, first list is 2 - 5 - 7 - 10 second list is 2 - 4 - 8 - 10 the list that would be returned is 2 - 10 I am getting nowhere with this.. What I have been think of was to check each value of the first list with each value of the second list recursively but the second list would then be cut by one node everytime and I cannot compare the next value in the first list with the the second list. I hope this makes sense... Can anyone help?

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  • Python - Flatten a dict of lists into unique values?

    - by Jonathan Vanasco
    I have a dict of lists in python: content = {88962: [80, 130], 87484: [64], 53662: [58,80]} I want to turn it into a list of the unique values [58,64,80,130] I wrote a manual solution, but it's a manual solution. I know there are more concise and more elegant way to do this with list comprehensions, map/reduce , itertools , etc. anyone have a clue ? content = {88962: [80, 130], 87484: [64], 53662: [58,80]} result = set({}) for k in content.keys() : for i in content[k]: result.add(i) # and list/sort/print just to compare the output r2 = list( result ) r2.sort() print r2

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  • What's the proper way of importing option lists into an Android app?

    - by Scott
    I have been storing option lists for my Android app in a cloud table. For example, categories like "historical fiction","biography","science fiction", etc. I see the following pros and cons: Pro: I can make changes to the list without sending an app update to Google Play Not normalized - I can use the text in my other data tables instead of a reference ID Con: App needs to take time to download from the web each time (or at least check for changes) English only I believe the "proper" way to do this is the use the XML resource files. But I need to make sure the selection references correctly with my data. That is, my app needs to understand that "Poetry" and "Poesía" are the same thing. Is the correct thing to do: Forget about it since I'll never get to the point where I'm translating my app anyway Use a string-array and use the index (0...x) to know what the selection is Use a 2-dimensional string-array with a reference ID in the first column and the text in the second?

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  • How do I avoid nesting forms when offering inline editing of lists with checkboxes for mass updates.

    - by adam
    A lot of sites offer the ability to edit lists of items inline as well as allowing multiple items to be selected via checkboxes and have an action performed all at once e.g. delete, mark as spam etc. But how do you implement this without violating html rules. I need one form for the checkboxes with individual submit_tags for the mass actions. But after a user clicks on an item in the list, another form via Ajax will be inserted within the checkbox form. How do I avoid doing this? I'm using rails and jQuery.

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  • How would I initialize these two lists so that modifying one doesn't modify the other?

    - by Brandon
    I'm aware of why this is happening, but is there any way to do this without having to implement ICloneable or a Copy() method? Preferably .net 2.0, but 3.5 is fine if it is necessary. Essentially I'm trying to implement an undo method. In most cases I can just perform the reverse action in the Undo(), but for others that is not possible. So I want to keep two lists. One for the list of items that I will be modifying, and one for the original, unmodified list of items. This way if I need to do an undo, I just delete the modified items and replace them with the originals. Most of the ways I've tried to assign the _originalItems variable doesn't work, so what would I need to do? public MyClass(List<SelectedItems> selectedItems) { _selectedItems = new List<SelectedItems>(selectedItems); _originalItems = ?? }

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  • How can I convert this string to list of lists?

    - by Phrixus
    Hi, what I'm trying to do is.. if a user types in [[0,0,0], [0,0,1], [1,1,0]] and press enter, the program should convert this string to several lists; one list holding [0][0][0], other for [0][0][1], and the last list for [1][1][0] I thought tuple thing would work out but no luck... :( I started phython yesterday -- (I'm C / C++ guy.) and cannot use the full advantages of this language... Does python have a good way to handle this? I need help~ :'(

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  • How do I remove initial indents on numbered lists?

    - by Peter
    In Word 2007 I want all numbers in a numbered list to be down the LH margin in line with the paragraphs. When a numbered list is selected, the numbers 1,2,3 are indented by a default 0.63cm. Ctrl-Shift-M will shift this indent back to the left margin. How do I permanently remove that initial indent and save that change to the normal template so that all new documents have zero indent on a newly inserted numbered list? (Same issue in Word 2010)

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  • Can Windows 7 Jump Lists be made to behave like menus when dragged out with a mouse?

    - by FocusStealer
    On a traditional menu, if you mousedown on the menu title, drag down, then release on a menu item, it will trigger that menu item immediately, e.g. in Notepad: Left mouse button down on File Drag down to New Release mouse button will start a new file without requiring an additional click. However, when dragging out a Jump List on Windows 7, you must additionally click the desired item to launch it. Is there any way to change this behavior?

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  • ASA firewalls: how does stateful filtering affect my access lists?

    - by Nate
    Ok, so assume that I have an ingress access list that looks like this: access-list outside_in extended ip permit any X.Y.Z.1 eq 25 access-group outside_in in interface outside And I want to do egress filtering. I want to allow inside machines to respond on port 80, and I want to allow ports over 1024. Given that the firewall is statefull, do I need to have the rule access-list inside_in extended ip permit X.Y.Z.1 any eq 25 in my inside_in ACL, or can I get away with just access-list inside_in extended ip permit any any gt 1024 access-group inside_in in interface inside In other words, if I apply an egress access list, do I have to explicitly allow machines to respond to requests allowed by the ingress access list, or does the statefullness of the firewall handle that for me? Thanks!

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  • Ldap access lists users even if user has no rights...

    - by Patkos Csaba
    I am trying to set up a more complex Active Directory structure for some testing purposes. What I did so far: set up 2 windows (one 2008 and one 2003) to control the same domain set up an Organizational Unit (ou): Developers set up 2 child OUs: "one" and "two" each OU has it's admin: adminOne and adminTwo I denied all access to OU "two" by removing on the Security tab all the groups I don't want to access it. now, when I log in as adminOne and I try to click on OU "two" it says I don't have permissions to see the users and properties of "two" - this is perfect, it's what I want Here comes my problem: I do a LDAP query with the adminOne user on the "Developers" What I expect to happen: I expect to retrieve the users from Developer - One I expect to NOT be able to retrieve the users from Developers - Two What actually happens: ldap shows all the users, both from Developers - One and Developers - Two, even if the user should not have permissions to Developers - Two And now my question: is there any specific settings on Windows 2003 or 2008 Active Directory servers which allow or deny access over LDAP? I could not find any.

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  • How to I create a user that is allowed to only add/remove users to distribution lists in Active Directory?

    - by Sorin Sbarnea
    I do have a third party product (Jira) that has Active Directory integration via LDAP. I want to enable Jira administrators to edit group memberships and have them syncronized inside Active Directory. This currently works but I needed to use a Domain Administrator service account in order to do this. The question is how can I do this without giving the entire Domain Administrator permission to the service account.

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  • what is the purpose of the files in this directory: /var/lib/apt/lists?

    - by Magpie
    linux lubuntu HD4000 intel ivy-bridge 8gb 1600 ram. I am getting a duplicate entry error message from synaptic package manager and it says the problem is there. I am wondering a few things: What this directory is. Whether it safe to simply delete the offending duplicates from there. Whether this is a useful new discovery... Is this where all the packages I have no use for end up and something I can edit to suit my fancy in the long run? It would be nice to be able to reduce the clutter in my package manager. Especially find a way to get rid of all the 32 bit stuff or older versions of programs I have downloaded manually elsewhere. I had meant to post this in linux! So if this is wrong place let me know and I will move it there!

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  • In JSF - What is the correct way to do this? Two dropdown lists with dependency.

    - by Ben
    Hi, I'm making two dropdown lists in JSF which are dependent. Specifically, one list has all the languages and the second list contains values that are displayed in the currently selected language. I've implemented this by having the second list use information from a Hash and rebuilding that Hash in the setter of the currently selected language. JSF Code Bit: <rich:dropDownMenu value="#{bean.currentlySelectedLanguage}" id="languageSelector"> ... (binding to languages hash) ... <rich:dropDownMenu value="#{bean.currentlySelectedScript}" id="ScriptPullDown"> ... (binding to scripts hash) ... Backing Bean Code Bit: setCurrentlySelectedLanguage(String lang){ this.currentlySelectedLanguage = lang; rebuildScriptNames(lang); } I'm wondering if that's a good way of doing this or if theres a better method that I am not aware of. Thank you! EDIT - Adding info.. I used a a4j:support that with event="onchange" and ReRender="ScriptPullDown" to rerender the script pull down. I could probably add an action expression to run a method when the value changes. But is there a benefit to doing this over using code in the setter function?

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  • How to compare 2 lists and merge them in Python/MySQL?

    - by NJTechGuy
    I want to merge data. Following are my MySQL tables. I want to use Python to traverse though a list of both Lists (one with dupe = 'x' and other with null dupes). For instance : a b c d e f key dupe -------------------- 1 d c f k l 1 x 2 g h j 1 3 i h u u 2 4 u r t 2 x From the above sample table, the desired output is : a b c d e f key dupe -------------------- 2 g c h k j 1 3 i r h u u 2 What I have so far : import string, os, sys import MySQLdb from EncryptedFile import EncryptedFile enc = EncryptedFile( os.getenv("HOME") + '/.py-encrypted-file') user = enc.getValue("user") pw = enc.getValue("pw") db = MySQLdb.connect(host="127.0.0.1", user=user, passwd=pw,db=user) cursor = db.cursor() cursor2 = db.cursor() cursor.execute("select * from delThisTable where dupe is null") cursor2.execute("select * from delThisTable where dupe is not null") result = cursor.fetchall() result2 = cursor2.fetchall() for cursorFieldname in cursor.description: for cursorFieldname2 in cursor2.description: if cursorFieldname[0] == cursorFieldname2[0]: ### How do I compare the record with same key value and update the original row null field value with the non-null value from the duplicate? Please fill this void... cursor.close() cursor2.close() db.close() Thanks guys!

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  • How can I restore the "auto" values with for list-style-type in nested unordered lists with CSS?

    - by Michael
    By default, an unstyled set of nested <ul> lists looks like this (in Chrome, Firefox, and IE at least): The top level has a list-style-type of disc, the next level is circle, and subsequent levels are square. If I include a stylesheet that changes the list-style-type to none, is there a simple way to revert back to the "automatic bullet types" later in the document? (e.g., override with a subsequent CSS definition or JavaScript style change) Basically, I'm looking for something like list-style-type: auto; (which is apparently not valid and has no effect): <style type="text/css"> ul { list-style-type: none; } ul { list-style-type: auto; } /* Does not work */ </style> Setting the list-style-type back to disc changes every bullet in the list and I no longer see different bullets at different levels, so that doesn't work either. Is the only way to accomplish this by explicitly defining styles for every level? e.g.: <style type="text/css"> ul { list-style-type: disc; } ul ul { list-style-type: circle; } ul ul ul { list-style-type: square; } </style>

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  • I'm doing a lot of lists and dictionary sorting...and this is causing memory errors in Python websit

    - by alex
    I retrieved data from the log table in my database. Then I started finding unique users, comparing/sorting lists, etc. In the end I got down to this. stats = {'2010-03-19': {'date': '2010-03-19', 'unique_users': 312, 'queries': 1465}, '2010-03-18': {'date': '2010-03-18', 'unique_users': 329, 'queries': 1659}, '2010-03-17': {'date': '2010-03-17', 'unique_users': 379, 'queries': 1845}, '2010-03-16': {'date': '2010-03-16', 'unique_users': 434, 'queries': 2336}, '2010-03-15': {'date': '2010-03-15', 'unique_users': 390, 'queries': 2138}, '2010-03-14': {'date': '2010-03-14', 'unique_users': 460, 'queries': 2221}, '2010-03-13': {'date': '2010-03-13', 'unique_users': 507, 'queries': 2242}, '2010-03-12': {'date': '2010-03-12', 'unique_users': 629, 'queries': 3523}, '2010-03-11': {'date': '2010-03-11', 'unique_users': 811, 'queries': 4274}, '2010-03-10': {'date': '2010-03-10', 'unique_users': 171, 'queries': 1297}, '2010-03-26': {'date': '2010-03-26', 'unique_users': 299, 'queries': 1617}, '2010-03-27': {'date': '2010-03-27', 'unique_users': 323, 'queries': 1310}, '2010-03-24': {'date': '2010-03-24', 'unique_users': 352, 'queries': 2112}, '2010-03-25': {'date': '2010-03-25', 'unique_users': 330, 'queries': 1290}, '2010-03-22': {'date': '2010-03-22', 'unique_users': 329, 'queries': 1798}, '2010-03-23': {'date': '2010-03-23', 'unique_users': 329, 'queries': 1857}, '2010-03-20': {'date': '2010-03-20', 'unique_users': 368, 'queries': 1693}, '2010-03-21': {'date': '2010-03-21', 'unique_users': 329, 'queries': 1511}, '2010-03-29': {'date': '2010-03-29', 'unique_users': 325, 'queries': 1718}, '2010-03-28': {'date': '2010-03-28', 'unique_users': 340, 'queries': 1815}, '2010-03-30': {'date': '2010-03-30', 'unique_users': 329, 'queries': 1891}} It's not a big dictionary. But when I try to do one last thing...it craps out on me. for k, v in stats: mylist.append(v) too many values to unpack What the heck does that mean??? TOO MANY VALUES TO UNPACK.

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  • How do I add two lists in Linq so addedList[x] = listOne[x] + listTwo[x]?

    - by Audie
    I want to add two lists of a numeric type such that addedList[x] = listOne[x] + listTwo[x] The output of the list needs to be a Generic.IEnumerable that I can use in future linq queries. While I was able to do it using the code below, I can't help but feel like there must be a better way. Any ideas? List<int> firstList = new List<int>(new int[] { 1, 3, 4, 2, 5, 7, 2, 5, 7, 8, 9, 0 }); List<int> secondList = new List<int>(new int[] { 4, 6, 8, 3, 1, 5, 9, 3, 0 }); int findex = 0; ILookup<int, int> flookup = firstList.ToLookup(f => { int i = findex; findex++; return i; }, p => p); var listsAdded = from grp in flookup select grp.First() + secondList.ElementAtOrDefault(grp.Key); foreach (int i in listsAdded) Console.WriteLine(i);

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  • Help with C# program design implementation: multiple array of lists or a better way?

    - by Bob
    I'm creating a 2D tile-based RPG in XNA and am in the initial design phase. I was thinking of how I want my tile engine to work and came up with a rough sketch. Basically I want a grid of tiles, but at each tile location I want to be able to add more than one tile and have an offset. I'd like this so that I could do something like add individual trees on the world map to give more flair. Or set bottles on a bar in some town without having to draw a bunch of different bar tiles with varying bottles. But maybe my reach is greater than my grasp. I went to implement the idea and had something like this in my Map object: List<Tile>[,] Grid; But then I thought about it. Let's say I had a world map of 200x200, which would actually be pretty small as far as RPGs go. That would amount to 40,000 Lists. To my mind I think there has to be a better way. Now this IS pre-mature optimization. I don't know if the way I happen to design my maps and game will be able to handle this, but it seems needlessly inefficient and something that could creep up if my game gets more complex. One idea I have is to make the offset and the multiple tiles optional so that I'm only paying for them when needed. But I'm not sure how I'd do this. A multiple array of objects? object[,] Grid; So here's my criteria: A 2D grid of tile locations Each tile location has a minimum of 1 tile, but can optionally have more Each extra tile can optionally have an x and y offset for pinpoint placement Can anyone help with some ideas for implementing such a design (don't need it done for me, just ideas) while keeping memory usage to a minimum? If you need more background here's roughly what my Map and Tile objects amount to: public struct Map { public Texture2D Texture; public List<Rectangle> Sources; //Source Rectangles for where in Texture to get the sprite public List<Tile>[,] Grid; } public struct Tile { public int Index; //Where in Sources to find the source Rectangle public int X, Y; //Optional offsets }

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  • What's the right way to do mutable data structures (e.g., skip lists, splay trees) in F#?

    - by dan
    What's a good way to implement mutable data structures in F#? The reason I’m asking is because I want to go back and implement the data structures I learned about in the algorithms class I took this semester (skip lists, splay trees, fusion trees, y-fast tries, van Emde Boas trees, etc.), which was a pure theory course with no coding whatsoever, and I figure I might as well try to learn F# while I’m doing it. I know that I “should” use finger trees to get splay tree functionality in a functional language, and that I should do something with laziness to get skip-list functionality, etc. , but I want to get the basics nailed down before I try playing with purely functional implementations. There are lots of examples of how to do functional data structures in F#, but there isn’t much on how to do mutable data structures, so I started by fixing up the doubly linked list here into something that allows inserts and deletes anywhere. My plan is to turn this into a skip list, and then use a similar structure (discriminated union of a record) for the tree structures I want to implement. Before I start on something more substantial, is there a better way to do mutable structures like this in F#? Should I just use records and not bother with the discriminated union? Should I use a class instead? Is this question "not even wrong"? Should I be doing the mutable structures in C#, and not dip into F# until I want to compare them to their purely functional counterparts? And, if a DU of records is what I want, could I have written the code below better or more idiomatically? It seems like there's a lot of redundancy here, but I'm not sure how to get rid of it. module DoublyLinkedList = type 'a ll = | None | Node of 'a ll_node and 'a ll_node = { mutable Prev: 'a ll; Element : 'a ; mutable Next: 'a ll; } let insert x l = match l with | None -> Node({ Prev=None; Element=x; Next=None }) | Node(node) -> match node.Prev with | None -> let new_node = { Prev=None; Element=x; Next=Node(node)} node.Prev <- Node(new_node) Node(new_node) | Node(prev_node) -> let new_node = { Prev=node.Prev; Element=x; Next=Node(node)} node.Prev <- Node(new_node) prev_node.Next <- Node(new_node) Node(prev_node) let rec nth n l = match n, l with | _,None -> None | _,Node(node) when n > 0 -> nth (n-1) node.Next | _,Node(node) when n < 0 -> nth (n+1) node.Prev | _,Node(node) -> Node(node) //hopefully only when n = 0 :-) let rec printLinkedList head = match head with | None -> () | Node(x) -> let prev = match x.Prev with | None -> "-" | Node(y) -> y.Element.ToString() let cur = x.Element.ToString() let next = match x.Next with | None -> "-" | Node(y) -> y.Element.ToString() printfn "%s, <- %s -> %s" prev cur next printLinkedList x.Next

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  • DataGrid : Binding with two different classes with lists ? WPF C#

    - by MyRestlessDream
    It is my first question on StackOverflow so I hope I am doing nothing wrong ! Sorry if it is the case ! I need some help because I can not find the solution of my problem. Of course I have searched everywhere on the web but I can not find it (can not post the links that I am using because of my low reputation :( ). Moreover, I am new in C# and WPF (and self-learning). I used to work in C++/Qt so I do not know how everything works in WPF. And sorry for my English, I am French. My problem My basic classes are that an Employee can use a computer. The id of the computer and the date of use are stored into the class Connection. I would like to display the list information in a DataGrid and in RowDetailsTemplate like here : http://i.stack.imgur.com/Bvn1z.png So it will do a binding to the Employee class but also to the Connection class with only the last value of the property (here the last value of the list "Computer ID" and the last value of the list "Connection Date" on this last computer). So it is a loop in the different lists. How can I do it ? Is it too much to do ? :( I succeed to get the Employee informations but I do not know how to bind the list of computer. When I am trying, it shows me "(Collection)" so it does not go inside the list :( Summary of Questions How to display/bind a value from a list AND from a different class in a DataGrid ? How to display all the values of a list into the RowDetailsTemplate ? Under Windows 7 and Visual Studio 2010 Pro version. ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ EDIT ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Solution I have used the solution of Stefan Denchev. Here the modification of my class : http://i.stack.imgur.com/Ijx5i.png And the code used: <DataGrid ItemsSource="{Binding}" Name="table"> <DataGrid.Columns> <DataGridTextColumn Header="First Name" Binding="{Binding FirstName}"/> <DataGridTextColumn Header="Last Name" Binding="{Binding LastName}"/> <DataGridTextColumn Header="Gender" Binding="{Binding Gender}"/> <DataGridTextColumn Header="Last computer used" Binding="{Binding LastComputerID}"/> <DataGridTextColumn Header="Last connection date" Binding="{Binding LastDate}"/> </DataGrid.Columns> <DataGrid.RowDetailsTemplate> <DataTemplate> <DataGrid ItemsSource="{Binding ListOfConnection}"> <DataGrid.Columns> <DataGridTextColumn Header="Computer ID" Binding="{Binding ComputerID}"/> <DataGridTemplateColumn> <DataGridTemplateColumn.CellTemplate> <DataTemplate> <ListView ItemsSource="{Binding ListOfDate}"/> </DataTemplate> </DataGridTemplateColumn.CellTemplate> </DataGridTemplateColumn> </DataGrid.Columns> </DataGrid> </DataTemplate> </DataGrid.RowDetailsTemplate> </DataGrid> With in code behind : List<Employee> allEmployees = WorkflowMgr.Instance.AllEmployees; table.DataContext = allEmployees; And it works ! I have tryed to improve my fake example :) Hope it will help to another developer !

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  • top-k selection/merge

    - by tcurdt
    I have n sorted lists. These lists are quite long (300000+ tuples). Selecting the top 10 of the individual lists is of course trivial - they are right at the head of the lists. Where it gets more interesting is when I want the top 10 of all the sorted lists. The question is whether there is an algorithm to calculate the combined top 10 having the correct order while cutting off the long tail of the lists. The goal is to reduce the required space. And if there is: How does one find the limit where is is safe to cut? Note: The actual counts are not important. Only the order is.

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