comparison

问题 I'm teaching myself Objective-C 2.0. I see from various code samples, the following two approaches to test if an object has been initialised. If that's not exactly what these tests do, please correct me. Can you please explain the difference between the following: if (!myObject) and if (myObject == nil) 回答1: All objects are set to nil in the alloc method (or to zero for instance variables). Both of your cases checks if the object is equal to nil (is not initialized) and both will work. They

问题 I want to know if my value is included in an interval consisting of the previous row and the next row. How to do it in Talend? I tried a tMemorizeRow function where I save 3 lines each time, but encountered a java.lang.NullPointerException exception as when I am on the first line it does not know the next row I saved. What am I missing? 回答1: You can try this : add a column "sequence" with value as Numeric.sequence("s1",1,1) to your data : this way you'll know this exact order between rows in

问题 My first XElement is: XElement sourceFile = new XElement("source", from o in Version1.Element("folder").Elements("folders").ElementAt(0).Elements("folder") where o.Name != null && o.Name == "folder" select new XElement("data", new XElement("name",(string) o.Attribute("name")), new XElement("filesCount", (string)o.Attribute("folderCount")), new XElement("filesCount", (string)o.Attribute("filesCount")) )); //,o) My second is: XElement targetFile = new XElement("target", from o in Version2

问题 I need to compare a value from an array with a list of possible results, and then return a value in a variable depending on whether the list is matched or not. i.e. I have an array called $ErroredBackup with a column "status" I need to compare each $ErroredBackup.Status with a list of possible numbers, and if it matches set a $output variable to Error. If it doesn't match, leave the $output variable as is (I set it to Pass to start with) I've tried using -contain , but that seems to be the

问题 I'm trying to compare two numbers in R as a part of a if-statement condition: (a-b) >= 0.5 In this particular instance, a = 0.58 and b = 0.08... and yet (a-b) >= 0.5 is false. I'm aware of the dangers of using == for exact number comparisons, and this seems related: (a - b) == 0.5) is false, while all.equal((a - b), 0.5) is true. The only solution I can think of is to have two conditions: (a-b) > 0.5 | all.equal((a-b), 0.5) . This works, but is that really the only solution? Should I just

问题 I'm just getting started with Google scripts and I'm trying to create a very basic script to help me understand the fundamentals. The script would look for the number 5 in cell E2 and then return a value of 5 if true or 10 if false. The issue I'm running into is that if I enter a 5 on E2 I do not get a 5 on E4. it always says 10 on E4. I have tried changing the operator to = and === as well as putting quotes ( "5" ) around the 5 to look for text rather than a number and can't get it to work.

问题 What is the associativity of comparison operators in Python? It is straightforward for three comparisons, but for more than that, I'm not sure how it does it. They don't seem to be right- or left-associative. For example: >>> 7410 >= 8690 <= -4538 < 9319 > -7092 False >>> (((7410 >= 8690) <= -4538) < 9319) > -7092 True So, not left-associative. >>> 81037572 > -2025 < -4722 < 6493 False >>> (81037572 > (-2025 < (-4722 < 6493))) True So it's not right-associative either. I have seen some places

问题 What would be the best (most elegant or performing) way of overloading the equality operator on a class containing only string attributes? Example: class MagicClass { public string FirstAttribute { get; set; } public string SecondAttribute { get; set; } public string ThirdAttribute { get; set; } public string FourthAttribute { get; set; } public string FifthAttribute { get; set; } } I know how to overload the operator itself, however, I am wondering about the following points: Is there a way

问题 This question already has answers here : Comparing Object properties using reflection (5 answers) Best way to compare two complex objects (15 answers) Closed 4 years ago . I have two objects of the same class: Car oldCar = new Car() { Engine = "V6", Wheels = 4 } Car newCar = new Car() { Engine = "V8" Wheels = 4 } I want to compare the properties of the two Car objects, and if different (like in the example), print the old and updated values, like this: Engine: V6 -> V8 The way I'm doing this

问题 var_dump("555555555555555555555" == "555555555555555555553"); //bool(true) var_dump("aaaaaaaaaaaaaaaaaaaaa" == "aaaaaaaaaaaaaaaaaaaab"); //bool(false) Why does this happen? I know I can use var_dump(strcmp("555555555555555555555", "555555555555555555553") == 0); //bool(false) But why the first row returns true ? 回答1: It's a side effect of type-coercing. There's an article on phpsadness about it. Basically, the strings in the comparison are converted to numeric types, and due to precision loss