evaluation

问题 With the introduction of Null-Conditional Operators in C#, for the following evaluation, if (instance != null && instance.Val != 0) If I rewrite it this way, if (instance?.Val != 0) it will be evaluated to true if instance is a null reference; It behaves like if (instance == null || instance.Val != 0) So what is the right way to rewrite the evaluation using this new syntax? Edit: instance is a field of a big object which is deserialized from JSON. There are quite a few pieces of code like

问题 How would I get something similar to the following?: (evaluate-text "(+ 1 2)") ; resolves to 3 回答1: (load-string "(+ 1 2)") 回答2: user> (eval (read-string "(+ 1 2)")) 3 You probably shouldn't ever need to do this. Macros and fns make this kind of thing unnecessary 99% of the time. This is quite brittle, and can be unsafe if these strings are coming from user input, and so on. 回答3: How similar does it have to be? Clojure's eval works on lists, so: (eval (list + 1 2)) #=> 3 来源： https:/

问题 Closed . This question is opinion-based. It is not currently accepting answers. Want to improve this question? Update the question so it can be answered with facts and citations by editing this post. Closed 2 months ago . I am working on regression problem and i used ad-boost with decision tree for regression and r^2 as evaluation measure. I want to know how much difference between training r^2 and testing r^2 is considered suitable. I have training r^2 is 0.9438 and testing r^2 is 0.877 . Is

问题 Closed . This question is opinion-based. It is not currently accepting answers. Want to improve this question? Update the question so it can be answered with facts and citations by editing this post. Closed 2 months ago . I am working on regression problem and i used ad-boost with decision tree for regression and r^2 as evaluation measure. I want to know how much difference between training r^2 and testing r^2 is considered suitable. I have training r^2 is 0.9438 and testing r^2 is 0.877 . Is

问题 I am working on a c++ web-based IDE for beginners where one of it's core function is to let the user know the evaluation result ( true or false ) of the conditional statement they have on my contenteditable div. Say i am already able to fetch the "fragment" (what i call it based on my architecture) that i wanted to evaluate and i already know the values of the variables... Can you please suggest a way on how would i evaluate the text on the fragment as a conditional statement that will return

问题 Issue I want to import a CSV file with mixed data types of numbers and variables/symbols. The import part was already discussed in Import CSV file with mixed data types. Description The CSV file here contains only 2x2 formulas (but in general 64x64 and I evaluate it 1'000'000 times). The problem that I was facing is the evaluation of the cells. This can not be done in the same way. The matlab code is something like % Parameter initialization vector1 = ones(1e6); a=1; b=2; c=3; d=4; % Formula

问题 OK, this might seem too tough to be posted here so I beg your pardon. Been working on this for almost a week. I need to extract all selected columns in a given Oracle SQL String. It should pass the following test cases: // single column test select col1 from dual // ^ should match "col1" // multiple column test select col1,col2 from dual // ^ should match "col1", "col2" // multiple space test select col1 , col2 from dual // ^ should match "col1", "col2" // "distinct" tests select distinct

问题 I'm doing some work evaluating log data that has been saved as JSON objects to a file. To facilitate my work I have created 2 small python scripts that filter out logged entries according to regular expressions and print out multiple fields from an event. Now I'd like to be able to evaluate simple mathematical operations when printing fields. This way I could just say something like ./print.py type download/upload and it would print the type and the upload to download ratio. My problem is

问题 I'm still working on a tiny parser for a tiny language defined in a task at school. The parser that generates an AST(Abstract syntax tree) is working. What I want is to check the defined variables, they must be bounded by the let expression. First the method that is defined in the task(suggestion, not needed): checkVars :: Expr -> Char data Expr = Var Char | Tall Int | Sum Expr Expr | Mult Expr Expr | Neg Expr | Let Expr Expr Expr deriving(Eq, Show) A valid sentence would be "let X be 5 in *

问题 mult is defined as a curried function: mult :: Int -> Int -> Int mult x = \y -> x * y In mult (1+2) (2+3) , what are the redex's. and are they mult(1+2) , 1+2 and 2+3 ? What is the outermost redex, and is it 2+3 ? Innermost evaluation works on the expression as following, according to Programming in Haskell by Hutton: mult (1+2) (2+3) = { applying the first + } mult 3 (2+3) = { applying mult } (\y -> 3 * y) (2+3) = { applying + } (\y -> 3 * y) 5 = { applying the lambda } 3 * 5 = { applying *