expression

问题 I want to create my custom expression for IQueryable. Sample extension method: public static IQueryable<T> GetByIntTest<T>(this IQueryable<T> qSource, Expression<Func<T, int?>> field, int? value) { if (value == null) return qSource; ConstantExpression constantExpression = Expression.Constant(value, typeof(int?)); BinaryExpression binaryExpression = Expression.Equal(field.Body, constantExpression); var predicate = Expression.Lambda<Func<T, bool>>(binaryExpression, field.Parameters); return

问题 As part of a Java assignment, I have to take an input arithmetic expression and store it in a binary tree. I have done everything necessary for the assignment except for the part where I read in the string of the expression and store it in the binary tree. I have created a class called BinaryTree. Its only field is a treenode called root. This treenode is defined as an innerclass in BinaryTree. It has 3 fields, a generic data field, and two children (left and right) that are type BinaryTree.

问题 I'm currently trying to parse math expression into expression tree. But I'm stuck on the stage where I need to implement functions and negates. I don't understand logic to do it using Shunting-Yard algorithm. What I currently want to do is to support Negates, like -(x+5) Function calls, like min(x,y) Power just after function name, like cos^2(x) Implicit multiplication, like 2x is same as 2*x Scientific notation Constants e and pi Can somebody tell me hints how to implement this? 回答1: An

问题 I'm currently trying to parse math expression into expression tree. But I'm stuck on the stage where I need to implement functions and negates. I don't understand logic to do it using Shunting-Yard algorithm. What I currently want to do is to support Negates, like -(x+5) Function calls, like min(x,y) Power just after function name, like cos^2(x) Implicit multiplication, like 2x is same as 2*x Scientific notation Constants e and pi Can somebody tell me hints how to implement this? 回答1: An

问题 I have been playing around with LINQ to Z3 for fun (not production use). I've ended up with this syntax as a start: var i = 123; var test2 = from t in TheormProver.NewTheorm() let f = TheormProver.Func<int, bool>() let a = TheormProver.Int let g = TheormProver.Func<bool, int>() where !f(a * 2) && g(f(g(f(4)))) == i * a && a < g(f(a)) select new { f = f.ToString(), g = g.ToString(), a, asd = "Test extra property" }; var solution = test2.Solve(); // Edited in for clarification // note that

问题 Is possible to convert a Predicate<T> to Expression<Func<T, bool>> in some way? I would like to use the next IQueryable function using the filters of the my ICollectionView: public static System.Linq.IQueryable<TSource> Where<TSource>(this System.Linq.IQueryable<TSource> source, System.Linq.Expressions.Expression<System.Func<TSource, bool>> predicate) Thanks 回答1: In theory it is possible to convert a delegate 'back' to an expression, because you can request the emitted IL of a delegate, which

问题 I need to write a regular expression for taking input like this 23,456,22,1,32767 i.e. No commas allowed at the start or end. Spaces may come before and/or start of comma for e.g. 23, 45,56 ,67 etc. Ranges of each number should be 0-32767. Currently I am using regular expression like this [0-9]+(,[0-9]+)* . This allows for numbers separated by commas only ( not allowing spaces at all), and it does not check for the range of number. 回答1: It's probably wise to do it in two steps. First check

问题 I would like to map a sequence of integers to a sequence of expression literals in order to use the latter as tick mark labels in a plot, e.g. lbls <- lapply(-2:2, function(i) expression(i * pi)) plot(...) axis(1, at=seq(-2,2)*pi, labels=lbls) So far I've tried all variations of bquote , substitute , expression etc. that I could think of, but apparently I must have missed something. Also, the FAQ and related SO questions & answers didn't fully solve this for me. How would I do it correctly (I

问题 I am trying to implement certain matrix operations but I am lost in the internals of ublas library. is there a resource such as tutorial or an example on how to implement new ublas matrix expressions? Thanks 回答1: Don't know if it'll help, but there's a wiki page on extending uBlas here. That expression template stuff really blows my mind. :) 回答2: My suggestion is to just template your new functions so you don't have to worry about matrix expressions or ublas internals. For example, if you

问题 Can you do an if-then-else statement inside a JSP expression? EDIT : Specifically I was looking for a JSP solution, not a JSTL solution. But some JSTL solutions below are highly rated and are very welcome. Just please do not vote me down for a duplicate question because one has already been asked about JSTL. 回答1: In JSP EL 2.0, you can do that using the ternary operator. For instance: <option value="1" ${param.number == 1 ? 'selected' : ''}>First option</option> What it does is it checks JSP