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  • Ruby RegEx not matching valid expression

    - by Matthew Carriere
    I have the following expression: ^\w(\s(+|-|\/|*)\s\w)*$ This simply looks to match a mathematical expression, where a user is prompted for terms separated by basic operators (ex: price + tax) The user may enter more than just 2 terms and one operator (ex: price + tax + moretax) I tested this expression in Rubular http://rubular.com/ With the terms: a + a (MATCH) a + a + a (MATCH) a + a + a + a a a + a a Everything works, but when I use it in Ruby it does not work! expression =~ /^\w(\s(+|-|\/|*)\s\w)*$/ I started picking the expression apart and noticed that if I remove the start of line caret it finds matches but isn't correct. a + a (MATCH) a a (MATCH) <-- this is not correct Why is this expression not working in Ruby code? (I am using Ruby 1.8.7 p174)

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  • Using multiple aggregate functions in an algebraic expression in (ANSI) SQL statement

    - by morpheous
    I have the following aggregate functions (AGG FUNCs): foo(), foobar(), fredstats(), barneystats(). I want to know if I can use multiple AGG FUNCs in an algebraic expression. This may seem a strange/simplistic question for seasoned SQL developers - however, the but the reason I ask is that so far, all AGG FUNCs examples I have seen are of the simplistic variety e.g. max(salary) < 100, rather than using the AGG FUNCs in an expression which involves using multiple AGG FUNCs in an expression (like agg_func1() agg_func2()). The information below should help clarify further. Given tables with the following schemas: CREATE TABLE item (id int, length float, weight float); CREATE TABLE item_info (item_id, name varchar(32)); # Is it legal (ANSI) SQL to write queries of this format ? SELECT id, name, foo, foobar, fredstats FROM A, B (SELECT id, foo(123) as foo, foobar('red') as foobar, fredstats('weight') as fredstats FROM item GROUP BY id HAVING [ALGEBRAIC EXPRESSION] ORDER BY id AS A), item_info AS B WHERE item.id = B.id Where: ALGEBRAIC EXPRESSION is the type of expression that can be used in a WHERE clause - for example: ((foo(x) < foobar(y)) AND foobar(y) IN (1,2,3)) OR (fredstats(x) <> 0)) I am using PostgreSQL as the db, but I would prefer to use ANSI SQL wherever possible. Assuming it is legal to include AGG FUNCS in the way I have done above, I'd like to know: Is there a more efficient way to write the above query ? Is there any way I can speed up the query in terms of a judicious choice of indexes on the tables item and item_info ? Is there a performance hit of using AGG FUNCs in an algebraic expression like I am (i.e. an expression involving the output of aggregate functions rather than constants? Can the expression also include 'scaled' AGG FUNC? (for example: 2*foo(123) < -3*foobar(456) ) - will scaling (i.e. multiplying an AGG FUNC by a number have an effect on performance?) How can I write the query above using INNER JOINS instead?

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  • All minimum spanning trees implementation

    - by russtbarnacle
    I've been looking for an implementation (I'm using networkx library.) that will find all the minimum spanning trees (MST) of an undirected weighted graph. I can only find implementations for Kruskal's Algorithm and Prim's Algorithm both of which will only return a single MST. I've seen papers that address this problem (such as http://fano.ics.uci.edu/cites/Publication/Epp-TR-95-50.html) but my head tends to explode someway through trying to think how to translate it to code. In fact i've not been able to find an implementation in any language!

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  • Using System.DateTime in a C# Lambda expression gives an exception

    - by Samantha J
    I tried to implement a suggestion that came up in another question: Stackoverflow question Snippet here: public static class StatusExtensions { public static IHtmlString StatusBox<TModel>( this HtmlHelper<TModel> helper, Expression<Func<TModel, RowInfo>> ex ) { var createdEx = Expression.Lambda<Func<TModel, DateTime>>( Expression.Property(ex.Body, "Created"), ex.Parameters ); var modifiedEx = Expression.Lambda<Func<TModel, DateTime>>( Expression.Property(ex.Body, "Modified"), ex.Parameters ); var a = "a" + helper.HiddenFor(createdEx) + helper.HiddenFor(modifiedEx); return new HtmlString( "Some things here ..." + helper.HiddenFor(createdEx) + helper.HiddenFor(modifiedEx) ); } } When implemented I am getting the following exception which I don't really understand. The exception points to the line starting with "var createdEx =" System.ArgumentException was unhandled by user code Message=Expression of type 'System.Nullable`1[System.DateTime]' cannot be used for return type 'System.DateTime' Source=System.Core StackTrace: Can anyone help me out and suggest what I could do to resolve the exception?

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  • Why do I get errors when using unsigned integers in an expression with C++?

    - by neuviemeporte
    Given the following piece of (pseudo-C++) code: float x=100, a=0.1; unsigned int height = 63, width = 63; unsigned int hw=31; for (int row=0; row < height; ++row) { for (int col=0; col < width; ++col) { float foo = x + col - hw + a * (col - hw); cout << foo << " "; } cout << endl; } The values of foo are screwed up for half of the array, in places where (col - hw) is negative. I figured because col is int and comes first, that this part of the expression is converted to int and becomes negative. Unfortunately, apparently it doesn't, I get an overflow of an unsigned value and I've no idea why. How should I resolve this problem? Use casts for the whole or part of the expression? What type of casts (C-style or static_cast<...)? Is there any overhead to using casts (I need this to work fast!)? EDIT: I changed all my unsigned ints to regular ones, but I'm still wondering why I got that overflow in this situation.

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  • Is there a Visual Studio (or freeware) equivalent for Expression Blend's "Edit Template" feature?

    - by DanM
    In Expression Blend, you can view and edit the control template of objects in the "Objects and Timeline" panel. I'm wondering if there's an equivalent feature in Visual Studio or if there's something free (or very inexpensive) I can download that will allow me to do this. Here's a screen cap from Expression Blend that shows what I'm talking about: Doing this for DataGrid results in the following: <Style x:Key="DataGridStyle1" TargetType="{x:Type Custom:DataGrid}"> ... <Setter Property="Template"> <Setter.Value> <ControlTemplate TargetType="{x:Type Custom:DataGrid}"> ... </ControlTemplate> </Setter.Value> </Setter> <Style.Triggers> <Trigger Property="IsGrouping" Value="True"> <Setter Property="ScrollViewer.CanContentScroll" Value="False"/> </Trigger> </Style.Triggers> </Style> (The ... is of course replaced with setters and the contents of the control template.) This is a very useful starting point if you want to create a custom style and template for a control. It seems like you can do pretty much anything you can do in Blend in Studio, but this one is eluding me. Any ideas? Edit I'm also curious if this feature will be in Visual Studio 2010. Anyone know?

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  • SSIS Expression Tester Tool

    - by Davide Mauri
    Thanks to my friend's Doug blog I’ve found a very nice tool made by fellow MVP Darren Green which really helps to make SSIS develoepers life easier: http://expressioneditor.codeplex.com/Wikipage?ProjectName=expressioneditor In brief the tool allow the testing of SSIS Expression so that one can evaluate and test them before using in SSIS packages. Cool and useful! Share this post: email it! | bookmark it! | digg it! | reddit! | kick it! | live it!

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  • SSIS Expression Tester Tool

    - by Davide Mauri
    Thanks to my friend's Doug blog I’ve found a very nice tool made by fellow MVP Darren Green which really helps to make SSIS develoepers life easier: http://expressioneditor.codeplex.com/Wikipage?ProjectName=expressioneditor In brief the tool allow the testing of SSIS Expression so that one can evaluate and test them before using in SSIS packages. Cool and useful! Share this post: email it! | bookmark it! | digg it! | reddit! | kick it! | live it!

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  • Assembly Resources Expression Builder

    - by João Angelo
    In ASP.NET you can tackle the internationalization requirement by taking advantage of native support to local and global resources used with the ResourceExpressionBuilder. But with this approach you cannot access public resources defined in external assemblies referenced by your Web application. However, since you can extend the .NET resource provider mechanism and create new expression builders you can workaround this limitation and use external resources in your ASPX pages much like you use local or global resources. Finally, if you are thinking, okay this is all very nice but where’s the code I can use? Well, it was too much to publish directly here so download it from Helpers.Web@Codeplex, where you also find a sample on how to configure and use it.

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  • Cooking with Expression: HTML 5 Video for All

    - by David Wesst
    Happy new year everyone! I hope you enjoy the first new episode of 2011. --- In today’s episode we will be cooking up some HTML 5 video. This recipe will let you deliver videos to your users using browsers that support HTML 5, and even handle those who have not made the jump to the latest and greatest browsers. Feel free to leave comments on the page. Feedback is always welcome. Cooking with Expression - HTML 5 Video for All from David Wesst on Vimeo.

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  • NetBeans "Find Usages" Tool Integrates JSF Expression Language

    - by Geertjan
    I saw this by Adam on Twitter today: Interesting. Let's try it. Here's my method "getCustomerId". I select it, right-click, and choose "Find Usages" (or press Alt-F7): A nice dialog appears: Then click "Find" and, guess what, this is what I see (click to enlarge it): Clearly, as you can see, I'm not only finding the Java controller class where the getter is used, but also the Facelets files, and, within those, the exact lines where the JSF expression language makes use of the getter. This is not a new feature, tried it and got the same result in 7.1.1, but it's really cool to know about nonetheless.

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  • Why Developers Should, Must, Do Care About The New Expression Blend

    Okay, tough love: if you are serious about Silverlight development, the days of using one Integrated Development Environment for all you work are. over.  The benefits of adding Expression Blend to your toolkit, and getting serious about learning how to use it well are so overwhelming that you can no longer afford to ignore them. [...]...Did you know that DotNetSlackers also publishes .net articles written by top known .net Authors? We already have over 80 articles in several categories including Silverlight. Take a look: here.

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  • MS SQL server and Trees

    - by Julian
    Im looking for some way of extrating data form a tree table as defined below. Table Tree Defined as :- TreeID uniqueidentifier TreeParent uniqueidentifier TreeCode varchar(50) TreeDesc varchar(100) Data some (23k rows), Parent Refs back into ID in table The following SQL renders the whole tree (takes arround 2 mins 30) I need to do the following. 1) Render each Tree Node with its LVL 1 parent 2) Render all nodes that have a Description that matches a TreeDesc like 'SomeText%' 3) Render all parent nodes that are for a single tree id. Items 2 and 3 take 2mins30 so this needs to be a lot faster! Item 1, just cant work out how to do it with out killing SQL or taking forever any sugestions would be helpfull Thanks Julian WITH TreeCTE(TreeCode, TreeDesc, depth, TreeParent, TreeID) AS ( -- anchor member SELECT cast('' as varchar(50)) as TreeCode , cast('Trees' as varchar(100)) as TreeDesc, cast('0' as Integer) as depth, cast('00000000-0000-0000-0000-000000000000' as uniqueidentifier) as TreeParent, cast('00000000-0000-0000-0000-000000000000' as uniqueidentifier) as TreeID UNION ALL -- recursive member SELECT s.TreeCode, s.TreeDesc, cte.depth+1, isnull(s.TreeParent, cast('00000000-0000-0000-0000-000000000000' as uniqueidentifier)), isnull(s.TreeID, cast('00000000-0000-0000-0000-000000000000' as uniqueidentifier)) FROM pdTrees AS S JOIN TreeCTE AS cte ON isnull(s.TreeParent, cast('00000000-0000-0000-0000-000000000000' as uniqueidentifier)) = isnull( cte.TreeID , cast('00000000-0000-0000-0000-000000000000' as uniqueidentifier)) ) -- outer query SELECT s.TreeID, s.TreeCode, s.TreeDesc, s.depth, s.TreeParent FROM TreeCTE s

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  • Reconstructing trees from a "fingerprint"

    - by awshepard
    I've done my SO and Google research, and haven't found anyone who has tackled this before, or at least, anyone who has written about it. My question is, given a "universal" tree of arbitrary height, with each node able to have an arbitrary number of branches, is there a way to uniquely (and efficiently) "fingerprint" arbitrary sub-trees starting from the "universal" tree's root, such that given the universal tree and a tree's fingerprint, I can reconstruct the original tree? For instance, I have a "universal" tree (forgive my poor illustrations), representing my universe of possibilities: Root / / / | \ \ ... \ O O O O O O O (Level 1) /|\/|\...................\ (Level 2) etc. I also have tree A, a rooted subtree of my universe Root / /|\ \ O O O O O / Etc. Is there a way to "fingerprint" the tree, so that given that fingerprint, and the universal tree, I could reconstruct A? I'm thinking something along the lines of a hash, a compression, or perhaps a functional/declarative construction? Big-O analysis (in time or space) is a plus. As a for-instance, a nested expression like: {{(Root)},{(1),(2),(3)},{(2,3),(1),(4,5)}...} representing the actual nodes present at each level in the tree is probably valid, but can it be done more efficiently?

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  • How to define trees with more than one type in ML programing language

    - by user550413
    Well, I am asked to do the next thing: To define a binary tree which can contain 2 different types: ('a,'b) abtree and these are the requirements: Any inner vertex (not a leaf) must be of the type 'a or 'b and the leafs have no value. For every path in the tree all 'a values must appear before the 'b value: examples of paths: 'a->'a->'a-'b (legal) 'a->'b->'b (legal) 'a->'a->'a (legal) 'b->'b->'b (legal) 'a->'b->'a (ILLEGAL) and also I need to define another tree which is like the one described above but now I have got also 'c and in the second requirement it says that for every path I 'a values appear before the 'b values and all the 'b values appear before the 'c values. First, I am not sure how to define binary trees to have more than 1 type in them. I mean the simplest binary tree is: datatype 'a tree = leaf | br of 'a * 'a tree * 'a tree; And also how I can define a tree to have these requirements. Any help will be appreciated. Thanks.

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  • Idea of an algorithm to detect a website's navigation structure?

    - by Uwe Keim
    Currently I am in the process of developing an importer of any existing, arbitrary (static) HTML website into the upcoming release of our CMS. While the downloading the files is solved successfully, I'm pulling my hair off when it comes to detect a site structure (pages and subpages) purely from the HTML files, without the user specifying additional hints. Basically I want to get a tree like: + Root page 1 + Child page 1 + Child page 2 + Child child page1 + Child page 3 + Root page 2 + Child page 4 + Root page 3 + ... I.e. I want to be able to detect the menu structure from the links inside the pages. This has not to be 100% accurate, but at least I want to achieve more than just a flat list. I thought of looking at multiple pages to see similar areas and identify these as menu areas and parse the links there, but after all I'm not that satisfied with this idea. My question: Can you imagine any algorithm when it comes to detecting such a structure? Update 1: What I'm looking for is not a web spider, but an algorithm do create a logical tree of the relationship of the pages to be able to create pages and subpages inside my CMS when importing them. Update 2: As of Robert's suggestion I'll solve this by starting at the root page, and then simply parse links as you go and treat every link inside a page simply as a child page. Probably I'll recurse not in a deep-first manner but rather in a breadth-first manner to get a more balanced navigation structure.

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  • Most efficient way to rebuild a tree structure from data

    - by Ahsan
    Have a question on recursively populating JsTree using the .NET wrapper available via NuGet. Any help would be greatly appreciated. the .NET class JsTree3Node has a property named Children which holds a list of JsTree3Nodes, and the pre-existing table which contains the node structure looks like this NodeId ParentNodeId Data AbsolutePath 1 NULL News /News 2 1 Financial /News/Financial 3 2 StockMarket /News/Financial/StockMarket I have a EF data context from the the database, so my code currently looks like this. var parentNode = new JsTree3Node(Guid.NewGuid().ToString()); foreach(var nodeItem in context.Nodes) { parentNode.Children.Add(nodeItem.Data); // What is the most efficient logic to do this recursively? } as the inline comment says in the above code, what would be the most efficient way to load the JStree data on to the parentNode object. I can change the existing node table to suite the logic so feel free to suggest any changes to improve performance.

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  • How exactly is an Abstract Syntax Tree created?

    - by Howcan
    I think I understand the goal of an AST, and I've build a couple of tree structures before, but never an AST. I'm mostly confused because the nodes are text and not number, so I can't think of a nice way to input a token/string as I'm parsing some code. For example, when I looked at diagrams of AST's, the variable and its value were leaf nodes to an equal sign. This makes perfect sense to me, but how would I go about implementing this? I guess I can do it case by case, so that when I stumble upon an "=" I use that as a node, and add the value parsed before the "=" as the leaf. It just seems wrong, because I'd probably have to make cases for tons and tons of things, depending on the syntax. And then I came upon another problem, how is the tree traversed? Do I go all the way down the height, and go back up a node when I hit the bottom, and do the same for it's neighbor? I've seen tons of diagrams on ASTs, but I couldn't find a fairly simple example of one in code, which would probably help.

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  • Count function on tree structure (non-binary)

    - by Spevy
    I am implementing a tree Data structure in c# based (largely on Dan Vanderboom's Generic implementation). I am now considering approach on handling a Count property which Dan does not implement. The obvious and easy way would be to use a recursive call which Traverses the tree happily adding up nodes (or iteratively traversing the tree with a Queue and counting nodes if you prefer). It just seems expensive. (I also may want to lazy load some of my nodes down the road). I could maintain a count at the root node. All children would traverse up to and/or hold a reference to the root, and update a internally settable count property on changes. This would push the iteration problem to when ever I want to break off a branch or clear all children below a given node. Generally less expensive, and puts the heavy lifting what I think will be less frequently called functions. Seems a little brute force, and that usually means exception cases I haven't thought of yet, or bugs if you prefer. Does anyone have an example of an implementation which keeps a count for an Unbalanced and/or non-binary tree structure rather than counting on the fly? Don't worry about the lazy load, or language. I am sure I can adjust the example to fit my specific needs. EDIT: I am curious about an example, rather than instructions or discussion. I know this is not technically difficult...

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  • Inexpensive generation of hierarchical unique IDs

    - by romaninsh
    My application is building a hierarchical structure like this: root = { 'id': 'root', 'children': [ { 'name': 'root_foo', 'children': [] }, { 'id': 'root_foo2', 'children': [ { 'id': 'root_foo2_bar', 'children': [] } ] } ] } in other words, it's a tree of nodes, where each node might have child elements and unique identifier I call "id". When a new child is added, I need to generate a unique identifier for it, however I have two problems: identifiers are getting too long adding many children takes slower, as I need to find first available id My requirement is: naming of a child X must be determined only from the state in their ancestors When I re-generate tree with same contents, the IDs must be same or in other words, when we have nodes A and B, creating child in A, must not affect the name given to children of B. I know that one way to optimize would be to introduce counter in each node and append it to the names which will solve my performance issue, but will not address the issue with the "long identifiers". Could you suggest me the algorithm for quickly coming up with new IDs?

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  • How should I create a mutable, varied jtree with arbitrary/generic category nodes?

    - by Pureferret
    Please note: I don't want coding help here, I'm on Programmers for a reason. I want to improve my program planning/writing skills not (just) my understanding of Java. I'm trying to figure out how to make a tree which has an arbitrary category system, based on the skills listed for this LARP game here. My previous attempt had a bool for whether a skill was also a category. Trying to code around that was messy. Drawing out my tree I noticed that only my 'leaves' were skills and I'd labeled the others as categories. Explanation of tree: The Tree is 'born' with a set of hard coded highest level categories (Weapons, Physical and Mental, Medical etc.). Fro mthis the user needs to be able to add a skill. Ultimately they want to add 'One-handed Sword Specialisation' for instance. To do so you'd ideally click 'add' with Weapons selected and then select One-handed from a combobox, then click add again and enter a name in a text field. Then click add again to add a 'level' or 'tier' first proficiency, then specialisation. Of course if you want to buy a different skill it's completely different, which is what I'm having trouble getting my head around let alone programming in. What is a good system for describing this sort of tree in code? All the other JTree examples I've seen have some predictable pattern, and I don't want to have to code this all in 'literals'. Should I be using abstract classes? Interfaces? How can I make this sort of cluster of objects extensible when I add in other skills not listed above that behave differently? If there is not a good system to use, if there a good process for working out how to do this sort of thing?

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  • Web Crawler for Learnign Topics on Wikipedia

    - by Chris Okyen
    When I want to learn a vast topic on wikipedia, I don't know where to start. For instance say I want to learn about Binary Stars, I then have to know other things linked on that pages and linked pages on all the linked pages and so on for the specified number of levels. I want to write a web crawler like HTTracker or something similiar, that will display a heiarchy of the links on a certain page and the links on those linked pages.I wish to use as much prewritten code as possible. Here is an example: Pretending we are bending the rules by grabing links from only the first sentence of each pages The example archives and "processes" two levels deep The page is Ternary operation The First Level In mathematics a ternary operation is an N-ary operation The Second Level Under Mathmatics: Mathematics (from Greek µ???µa máthema, “knowledge, study, learning”) is the abstract study of topics encompassing quantity, structure, space, change and others; it has no generally accepted definition. Under N-ary In logic,mathematics, and computer science, the arity i/'ær?ti/ of a function or operation is the number of arguments or operands that the function takes Under Operation In its simplest meaning in mathematics and logic, an operation is an action or procedure which produces a new value from one or more input values ------------------------------------------------------------------------- I need some way to determine what oder to approach all these wiki pages to learn the concept ( in this case ternary operations )... Following along with this exmpakle, one way to show the path to read would a printout flowout like so: This shows that the first sentence of the Mathematics page doesn't link to the first sentence of pages linked on ternary page two levels deep. (Please tell me how I should explain this ) --- In otherwords, the child node of the top pages first sentence, ternary_operation, does not have any child nodes that reference the children of the top pages other children nodes- N-ary and operation. Thus it is safe to read this first. Since N-ary has a link to operations we shoudl read the operation page second and finally read the N-ary page last. Again, I wish to use as much prewritten code as possible, and was wondering what language to use and what would be the simpliest way to go about doing this if there isn't already somethign out there? Thank You!

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  • Performing a Depth First Search iteratively using async/parallel processing?

    - by Prabhu
    Here is a method that does a DFS search and returns a list of all items given a top level item id. How could I modify this to take advantage of parallel processing? Currently, the call to get the sub items is made one by one for each item in the stack. It would be nice if I could get the sub items for multiple items in the stack at the same time, and populate my return list faster. How could I do this (either using async/await or TPL, or anything else) in a thread safe manner? private async Task<IList<Item>> GetItemsAsync(string topItemId) { var items = new List<Item>(); var topItem = await GetItemAsync(topItemId); Stack<Item> stack = new Stack<Item>(); stack.Push(topItem); while (stack.Count > 0) { var item = stack.Pop(); items.Add(item); var subItems = await GetSubItemsAsync(item.SubId); foreach (var subItem in subItems) { stack.Push(subItem); } } return items; } I was thinking of something along these lines, but it's not coming together: var tasks = stack.Select(async item => { items.Add(item); var subItems = await GetSubItemsAsync(item.SubId); foreach (var subItem in subItems) { stack.Push(subItem); } }).ToList(); if (tasks.Any()) await Task.WhenAll(tasks); The language I'm using is C#.

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  • Traverse tree with results. Maybe type in Java?

    - by Angelo.Hannes
    I need to check a tree's node state. It can either be OK or NOT_OK. But that state is dependent on its children. So for a node to be OK, every of its children needs to be OK. If one or more of its children is NOT_OK the whole node is NOT_OK. To determine the state of a node I need to aggregate some properties of the node. So I thought of two possible implementations. And they are more or less covered in this question: Why is Option/Maybe considered a good idea and checked exceptions are not? Exception I could pass the properties up the recursion path, and throw an exception if something went wrong. Maybe I implement an Maybe type and let it either hold an error or the aggregated properties. Maybe it is more an Either. I tend towards the last option. And I'm thinking of an enum with two objects. Where I can additionally set those aggregated properties. Am I on the right track? I'm not familiar with the new JDK8 functional stuff. But I'm stuck on JDK7 anyway, so please focus on JDK7.

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