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  • Adding LambaExpression to an instance of IQueryable

    - by Paul Knopf
    ParameterExpression parameter = Expression.Parameter(typeof(Product), "x"); MemberExpression Left = Expression.MakeMemberAccess(parameter, typeof(Product).GetProperty("Name")); ConstantExpression Right = Expression.Constant(value, typeof(String)); BinaryExpression expression = Expression.Equal(Left, Right); LambdaExpression lambada = Expression.Lambda<Func<Product, bool>>(expression, parameter); Now how do I add this lambada to an instance of an IQuerybale, lets say _query _query.Where(lambada.Compile());?

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  • C++ Expression Templates

    - by yCalleecharan
    Hi, I currently use C for numerical computations. I've heard that using C++ Expression Templates is better for scientific computing. What are C++ Expression Templates in simple terms? Are there books around that discuss numerical methods/computations using C++ Expression Templates? In what way, C++ Expression Templates are better than using pure C? Thanks a lot

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  • How to write this in better way?

    - by dario
    Hi all. Let's look at this code: IList<IHouseAnnouncement> list = new List<IHouseAnnouncement>(); var table = adapter.GetData(); //get data from repository object -> DataTable if (table.Rows.Count >= 1) { for (int i = 0; i < table.Rows.Count-1; i++) { var anno = new HouseAnnouncement(); anno.Area = float.Parse(table.Rows[i][table.powierzchniaColumn].ToString()); anno.City = table.Rows[i][table.miastoColumn].ToString(); list.Add(anno); } } return list; Is it better way to write this in less code and better fashion (must be :-) )? Maybe using labda (but let mi know how)? Thanks in advance!

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  • negative look ahead to exclude html tags

    - by Remoh
    I'm trying to come up with a validation expression to prevent users from entering html or javascript tags into a comment box on a web page. The following works fine for a single line of text: ^(?!.(<|)).$ ..but it won't allow any newline characters because of the dot(.). If I go with something like this: ^(?!.(<|))(.|\s)$ it will allow multiple lines but the expression only matches '<' and '' on the first line. I need it to match any line. This works fine: ^[-_\s\d\w"'.,:;#/&\$\%\?!@+*\()]{0,4000}$ but it's ugly and I'm concerned that it's going to break for some users because it's a multi-lingual application. Any ideas? Thanks!

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  • Using a message class static method taking in an action to wrap Try/Catch

    - by Chris Marisic
    I have a Result object that lets me pass around a List of event messages and I can check whether an action was successful or not. I've realized I've written this code in alot of places Result result; try { //Do Something ... //New result is automatically a success for not having any errors in it result = new Result(); } catch (Exception exception) { //Extension method that returns a Result from the exception result = exception.ToResult(); } if(result.Success) .... What I'm considering is replacing this usage with public static Result CatchException(Action action) { try { action(); return new Result(); } catch (Exception exception) { return exception.ToResult(); } } And then use it like var result = Result.CatchException(() => _model.Save(something)); Does anyone feel there's anything wrong with this or that I'm trading reusability for obscurity?

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  • passing Func<TSource, TKey> keySelector error

    - by user338429
    static void Main() { string[] a = { "a", "asd", "bdfsd", "we" }; a = a.OrderBy(fun).ToArray(); } private static int fun(string s) { return s.Length; } its is giving compile time error . I know that we can do this with Lambda expression like this. a.OrderBy(s=>s.Length).ToArray(); but i want to this do by defining different function . What mistake i have done?

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  • check that int array contains !=0 value using lambda

    - by netmajor
    hey, I have two-dimension array List<List<int>> boardArray How can I enumerate throw this array to check that it contains other value than 0 ? I think about boardArray.Contains and ForEach ,cause it return bool value but I don't have too much experience with lambda expression :/ Please help :)

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  • PHP preg_match, need some help

    - by SoLoGHoST
    Can someone please help me with this preg_match if (preg_match('~[^A-Za-z0-9_\./\]~', $filepath)) // Show Error message. I need to match a possible filepath. So I need to check for double slashes, etc. Valid file path strings should look like this only: mydir/aFile.php or mydir/another_dir/anyfile.js So a slash at the beginning of this string should be checked also. Please help. Thanks :)

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  • Dynamic "WHERE IN" on IQueryable (linq to SQL)

    - by user320235
    I have a LINQ to SQL query returning rows from a table into an IQueryable object. IQueryable<MyClass> items = from table in DBContext.MyTable select new MyClass { ID = table.ID, Col1 = table.Col1, Col2 = table.Col2 } I then want to perform a SQL "WHERE ... IN ...." query on the results. This works fine using the following. (return results with id's ID1 ID2 or ID3) sQuery = "ID1,ID2,ID3"; string[] aSearch = sQuery.Split(','); items = items.Where(i => aSearch.Contains(i.ID)); What I would like to be able to do, is perform the same operation, but not have to specify the i.ID part. So if I have the string of the field name I want to apply the "WHERE IN" clause to, how can I use this in the .Contains() method?

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  • Is there such a thing as a MemberExpression that handles a many-to-many relationship?

    - by Jaxidian
    We're trying to make it easy to write strongly-typed code in all areas of our system, so rather than setting var sortColumn = "FirstName" we'd like to say sortOption = (p => p.FirstName). This works great if the sortOption is of type Expression<Func<Person, object>> (we actually use generics in our code but that doesn't matter). However, we run into problems for many-to-many relationships because this notation breaks down. Consider this simple code: internal class Business { public IQueryable<Address> Addresses { get; set; } public string Name { get; set; } } internal class Address { public State MyState { get; set; } } internal class State { public string Abbreviation { get; set; } public int StateID { get; set; } } Is it possible to have this sort of MemberExpression to identify the StateID column off of a business? Again, the purpose of using this is not to return a StateID object, it's to just identify that property off of that entity (for sorting, filtering, and other purposes). It SEEMS to me that there should be some way to do this, even if it's not quite as pretty as foo = business.Addresses.SomeExtension(a => a.State.StateID);. Is this really possible? If more background is needed, take a look at this old question of mine. We've since updated the code significantly, but this should give you the general detailed idea of the context behind this question.

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  • Regex: Match opening/closing chars with spaces

    - by Israfel
    I'm trying to complete a regular expression that will pull out matches based on their opening and closing characters, the closest I've gotten is ^(\[\[)[a-zA-Z.-_]+(\]\]) Which will match a string such as "[[word1]]" and bring me back all the matches if there is more than one, The problem is I want it to pick up matchs where there may be a space in so for example "[[word1 word2]]", now this will work if I add a space into my pattern above however this pops up a problem that it will only get one match for my entire string so for example if I have a string "Hi [[Title]] [[Name]] [[surname]], How are you" then the match will be "[[Title]] [[Name]] [[surname]]" rather than 3 matches "[[Title]]", "[[Name]]", "[[surname]]". I'm sure I'm just a char or two away in the Regex but I'm stuck, How can I make it return the 3 matches. Thanks

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  • RegEx - Time Validation ((h)h:mm)

    - by Josh
    /^\d{1,2}[:][0-5][0-9]$/ is what I have. this limits minutes to 00-59. It does not, however, limit hours to between 0 and 12. For similarity and uniformity I would like to do this with RegEx alone if possible. Further-more I would like the first digit to be optional. i.e. 09:30 accepted as well as 9:30. I played around with ranges, but something out of range is always acceptable.

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  • urgent..haskell mini interpreter

    - by mohamed elshikh
    i'm asked to implement this project and i have problems in part b which is the eval function this is the full describtion of the project You are required to implement an interpreter for mini-Haskell language. An interpreter is dened in Wikipedia as a computer program that executes, i.e. performs, instructions written in a programming language. The interpreter should be able to evaluate functions written in a special notation, which you will dene. A function is dened by: Function name Input Parameters : dened as a list of variables. The body of the function. The body of the function can be any of the following statements: a) Variable: The function may return any of the input variables. b) Arithmetic Expressions: The arithmetic expressions include input variables and addition, sub- traction, multiplication, division and modulus operations on arithmetic expressions. c) Boolean Expressions: The Boolean expressions include the ordering of arithmetic expressions (applying the relationships: <, =<, , = or =) and the anding, oring and negation of Boolean expressions. d) If-then-else statements: where the if keyword is followed by a Boolean expression. The then and else parts may be followed by any of the statements described here. e) Guarded expressions: where each case consists of a boolean expression and any of the statements described here. The expression consists of any number of cases. The rst case whose condition is true, its body should be evaluated. The guarded expression has to terminate with an otherwise case. f) Function calls: the body of the function may have a call to another function. Note that all inputs passed to the function will be of type Int. The output of the function can be of type Int or Bool. To implement the interpreter, you are required to implement the following: a) Dene a datatype for the following expressions: Variables Arithmetic expressions Boolean expressions If-then-else statements Guarded expressions Functions b) Implement the function eval which evaluates a function. It takes 3 inputs: The name of a function to be evaluated represented as a string. A list of inputs to that function. The arguments will always be of datatype Int. A list of functions. Each function is represented as instance of the datatype that you have created for functions. c) Implement the function get_type that returns the type of the function (as a string). The input to this function is the same as in part b. here is what i've done data Variable = v(char) data Arth= va Variable | Add Arth Arth | Sub Arth Arth | Times Arth Arth | Divide Arth Arth data Bol= Great Arth Arth | Small Arth Arth | Geq Arth Arth | Seq Arth Arth | And Bol Bol | Or Bol Bol | Neg Bol data Cond = data Guard = data Fun =cons String [Variable] Body data Body= bodycons(String) |Bol |Cond |Guard |Arth

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  • How do I test against a large number of regular expressions quickly and know which one matched?

    - by Jack
    I'm writing a program in .net where the user may provide a large number of regular expressions. For a given string, I need to figure out which regular expression matches that string (if more than one matches, I just need the first one that matches). However, if there are a large number of regular expressions this operation can take a very long time. I was somewhat hoping there would be something similar to flex for .net that would allow me to specify a large number of regular expressions yet quickly (O(n) according to Wikipedia for n = len(input string)) figure out which regular expression matches. Also, I would prefer not to implement my own regular expression engine :).

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  • Why are regular expressions such a complicated, cryptic mess?

    - by steffenj
    Often when I see regular expressions, I only see a total mess of characters. Why does it have to be this way? I guess what I really want to know is: are there alternatives to regular expressions that basically do the same thing but are implemented in a human readable language? [UPDATE] Thanks for all the great responses and inspiration! I wanted to highlight this particular link which shows how a (working) alternative would look like, which may also be a good starting point for learning or "simple" regex expressions. But you also quickly get a feel for the verbosity tradeoff.

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  • What is the role of `while`-loops in computation expressions in F#?

    - by MizardX
    If you define a While method of the builder-object, you can use while-loops in your computation expressions. The signature of the While method is: member b.While (predicate:unit->bool, body:M<'a>) : M<'a> For comparison, the signature of the For method is: member b.For (items:seq<'a>, body:unit->M<'a>) : M<'a> You should notice that, in the While-method, the body is a simple type, and not a function as in the For method. You can embed some other statements, like let and function-calls inside your computation-expressions, but those can impossibly execute in a while-loop more than once. builder { while foo() do printfn "step" yield bar() } Why is the while-loop not executed more than once, but merely repeated? Why the significant difference from for-loops? Better yet, is there some intended strategy for using while-loops in computation-expressions?

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  • Different Not Automatically Implies Better

    - by Alois Kraus
    Originally posted on: http://geekswithblogs.net/akraus1/archive/2013/11/05/154556.aspxRecently I was digging deeper why some WCF hosted workflow application did consume quite a lot of memory although it did basically only load a xaml workflow. The first tool of choice is Process Explorer or even better Process Hacker (has more options and the best feature copy&paste does work). The three most important numbers of a process with regards to memory are Working Set, Private Working Set and Private Bytes. Working set is the currently consumed physical memory (parts can be shared between processes e.g. loaded dlls which are read only) Private Working Set is the physical memory needed by this process which is not shareable Private Bytes is the number of non shareable which is only visible in the current process (e.g. all new, malloc, VirtualAlloc calls do create private bytes) When you have a bigger workflow it can consume under 64 bit easily 500MB for a 1-2 MB xaml file. This does not look very scalable. Under 64 bit the issue is excessive private bytes consumption and not the managed heap. The picture is quite different for 32 bit which looks a bit strange but it seems that the hosted VB compiler is a lot less memory hungry under 32 bit. I did try to repro the issue with a medium sized xaml file (400KB) which does contain 1000 variables and 1000 if which can be represented by C# code like this: string Var1; string Var2; ... string Var1000; if (!String.IsNullOrEmpty(Var1) ) { Console.WriteLine(“Var1”); } if (!String.IsNullOrEmpty(Var2) ) { Console.WriteLine(“Var2”); } ....   Since WF is based on VB.NET expressions you are bound to the hosted VB.NET compiler which does result in (x64) 140 MB of private bytes which is ca. 140 KB for each if clause which is quite a lot if you think about the actually present functionality. But there is hope. .NET 4.5 does allow now C# expressions for WF which is a major step forward for all C# lovers. I did create some simple patcher to “cross compile” my xaml to C# expressions. Lets look at the result: C# Expressions VB Expressions x86 x86 On my home machine I have only 32 bit which gives you quite exactly half of the memory consumption under 64 bit. C# expressions are 10 times more memory hungry than VB.NET expressions! I wanted to do more with less memory but instead it did consume a magnitude more memory. That is surprising to say the least. The workflow does initialize in about the same time under x64 and x86 where the VB code does it in 2s whereas the C# version needs 18s. Also nearly ten times slower. That is a too high price to pay for any bigger sized xaml workflow to convert from VB.NET to C# expressions. If I do reduce the number of expressions to 500 then it does need 400MB which is about half of the memory. It seems that the cost per if does rise linear with the number of total expressions in a xaml workflow.  Expression Language Cost per IF Startup Time C# 1000 Ifs x64 1,5 MB 18s C# 500 Ifs x64 750 KB 9s VB 1000 Ifs x64 140 KB 2s VB 500 Ifs x64 70 KB 1s Now we can directly compare two MS implementations. It is clear that the VB.NET compiler uses the same underlying structure but it has much higher offset compared to the highly inefficient C# expression compiler. I have filed a connect bug here with a harsher wording about recent advances in memory consumption. The funniest thing is that one MS employee did give an Azure AppFabric demo around early 2011 which was so slow that he needed to investigate with xperf. He was after startup time and the call stacks with regards to VB.NET expression compilation were remarkably similar. In fact I only found this post by googling for parts of my call stacks. … “C# expressions will be coming soon to WF, and that will have different performance characteristics than VB” … What did he know Jan 2011 what I did no know until today? ;-). He knew that C# expression will come but that they will not be automatically have better footprint. It is about time to fix that. In its current state C# expressions are not usable for bigger workflows. That also explains the headline for today. You can cheat startup time by prestarting workflows so that the demo looks nice and snappy but it does hurt scalability a lot since you do need much more memory than necessary. I did find the stacks by enabling virtual allocation tracking within XPerf which is still the best tool out there. But first you need to look at your process to check where the memory is hiding: For the C# Expression compiler you do not need xperf. You can directly dump the managed heap and check with a profiler of your choice. But if the allocations are happening on the Private Data ( VirtualAlloc ) you can find it with xperf. There is a nice video on channel 9 explaining VirtualAlloc tracking it in greater detail. If your data allocations are on the Heap it does mean that the C/C++ runtime did create a heap for you where all malloc, new calls do allocate from it. You can enable heap tracing with xperf and full call stack support as well which is doable via xperf like it is shown also on channel 9. Or you can use WPRUI directly: To make “Heap Usage” it work you need to set for your executable the tracing flags (before you start it). For example devenv.exe HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows NT\CurrentVersion\Image File Execution Options\devenv.exe DWORD TracingFlags 1 Do not forget to disable it after you did complete profiling the process or it will impact the startup time quite a lot. You can with xperf attach directly to a running process and collect heap allocation information from a gone wild process. Very handy if you need to find out what a process was doing which has arrived in a funny state. “VirtualAlloc usage” does work without explicitly enabling stuff for a specific process and is always on machine wide. I had issues on my Windows 7 machines with the call stack collection and the latest Windows 8.1 Performance Toolkit. I was told that WPA from Windows 8.0 should work fine but I do not want to downgrade.

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  • What's a good library for parsing mathematical expressions in java?

    - by CSharperWithJava
    I'm an Android Developer and as part of my next app I will need to evaluate a large variety of user created mathematical expressions and equations. I am looking for a good java library that is lightweight and can evaluate mathematical expressions using user defined variables and constants, trig and exponential functions, etc. I've looked around and Jep seems to be popular, but I would like to hear more suggestions, especially from people who have used these libraries before.

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  • RegexClean Transformation

    Use the power of regular expressions to cleanse your data right there inside the Data Flow. This transformation includes a full user interface for simple configuration, as well as advanced features such as error output configuration. Two regular expressions are used, a match expression and a replace expression. The transformation is designed around the named capture groups or match groups, and even supports multiple expressions. This allows for rich and complex expressions to be built, all through an easy to reuse transformation where a bespoke Script Component was previously the only alternative. Some simple properties are available for each column selected – Behaviour The two behaviour modes offer similar functionality but with a difference. Replace, replaces tokens with the input, and Emit overwrites the whole string. Cascade Cascade allows you to define multiple expressions, each on a new line. The match expression will be processed into one operation per line, which are then processed in order at run-time. Multiple replace expressions can also be specified, again each on a new line. If there is no corresponding replace expression for a match expression line, then the last replace expression will be used instead. It is common to have multiple match expressions, but only a single replace expression. Match Expression The expression used to define the named capture groups. This is where you can analyse the data, and tag or name elements within it as found by the match expression. Replace Expression The replace determines the final output. It will reference the named groups from the match expression and assembles them into the final output. If you want to use regular expressions to validate data then try the Regular Expression Transformation. Quick Start Guide Select a column. A new output column is created for each selected column; there is no option for in-place replacement of column values. One input column can be used to populate multiple output columns, just select the column again in the lower grid, using the Input Columns drop-down selector. Amend the output column name and size as required. They default to the same as the input column selected. Amend the behaviour as required, the default is Replace. Amend the cascade option as required, the default is true. Finally enter your match and replace regular expressions Quick Sample #1 Parse an email address and extract the user and domain portions. Format as a web address passing the user portion as a URL parameter. This uses two match groups, user and host, which correspond to the text before the @ and after it respectively. Behaviour is Emit, and cascade of false, we only have a single match expression. Match Expression ^(?<user>[^@]+)@(?<host>.+)$ Replace Expression - http://www.${host}?user=${user} Results Sample Input Sample Output [email protected] http://www.adventure-works.com?user=zheng0 The component is provided as an MSI file, however to complete the installation, you will have to add the transformation to the Visual Studio toolbox manually. Right-click the toolbox, and select Choose Items.... Select the SSIS Data Flow Items tab, and then check the RegexClean Transformation from the list. Downloads The RegexClean Transformation is available for both SQL Server 2005 and SQL Server 2008. Please choose the version to match your SQL Server version, or you can install both versions and use them side by side if you have both SQL Server 2005 and SQL Server 2008 installed. RegexClean Transformation for SQL Server 2005 RegexClean Transformation for SQL Server 2008 Version History SQL Server 2005 Version 1.0.0.105 - Public Release (28 Jan 2008) SQL Server 2005 Version 1.0.0.105 - Public Release (28 Jan 2008) Screenshot

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  • Is it safe to read regular expressions from a file?

    - by Zilk
    Assuming a Perl script that allows users to specify several text filter expressions in a config file, is there a safe way to let them enter regular expressions as well, without the possibility of unintended side effects or code execution? Without actually parsing the regexes and checking them for problematic constructs, that is. There won't be any substitution, only matching. As an aside, is there a way to test if the specified regex is valid before actually using it? I'd like to issue warnings if something like /foo (bar/ was entered. Thanks, Z. EDIT: Thanks for the very interesting answers. I've since found out that the following dangerous constructs will only be evaluated in regexes if the use re 'eval' pragma is used: (?{code}) (??{code}) ${code} @{code} The default is no re 'eval'; so unless I'm missing something, it should be safe to read regular expressions from a file, with the only check being the eval/catch posted by Axeman. At least I haven't been able to hide anything evil in them in my tests. Thanks again. Z.

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  • Efficient way to remove empty lists from lists without evaluating held expressions?

    - by Alexey Popkov
    In previous thread an efficient way to remove empty lists ({}) from lists was suggested: Replace[expr, x_List :> DeleteCases[x, {}], {0, Infinity}] Using the Trott-Strzebonski in-place evaluation technique this method can be generalized for working also with held expressions: f1[expr_] := Replace[expr, x_List :> With[{eval = DeleteCases[x, {}]}, eval /; True], {0, Infinity}] This solution is more efficient than the one based on ReplaceRepeated: f2[expr_] := expr //. {left___, {}, right___} :> {left, right} But it has one disadvantage: it evaluates held expressions if they are wrapped by List: In[20]:= f1[Hold[{{}, 1 + 1}]] Out[20]= Hold[{2}] So my question is: what is the most efficient way to remove all empty lists ({}) from lists without evaluating held expressions? The empty List[] object should be removed only if it is an element of another List itself. Here are some timings: In[76]:= expr = Tuples[Tuples[{{}, {}}, 3], 4]; First@Timing[#[expr]] & /@ {f1, f2, f3} pl = Plot3D[Sin[x y], {x, 0, Pi}, {y, 0, Pi}]; First@Timing[#[pl]] & /@ {f1, f2, f3} Out[77]= {0.581, 0.901, 5.027} Out[78]= {0.12, 0.21, 0.18} Definitions: Clear[f1, f2, f3]; f3[expr_] := FixedPoint[ Function[e, Replace[e, {a___, {}, b___} :> {a, b}, {0, Infinity}]], expr]; f1[expr_] := Replace[expr, x_List :> With[{eval = DeleteCases[x, {}]}, eval /; True], {0, Infinity}]; f2[expr_] := expr //. {left___, {}, right___} :> {left, right};

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