identifier

问题 Let's say I have the following data frame: a <- runif(10) dd <- as.data.frame(t(a)) names(dd) <- c("ID", "a", "a2", "b", "b2", "f", "XXX", "1", "4", "8") In dplyr , there is a nice way to select a number of columns. For example, to select the columns between column a and column f , I can use dd %>% dplyr::select(a:f) In my problem, the columns of the last part of the data frame may vary, yet they always have as name a number between 1 and 99. However, I can not seem to be able to do the same

问题 package main import "fmt" const name = "Yosua" // or var name string = "James" func main() { name := "Jobs" fmt.Println(name) } How to refer to the constant and not the the function level variable? 回答1: You can't. While the local variable name is in scope, the name name denotes the local variable. And there is no "qualifier" to refer to top-level identifiers. Spec: Declarations and scope: An identifier declared in a block may be redeclared in an inner block. While the identifier of the inner

问题 The problem I'm looking for feedback on this exploration of a locally unique alternative for GUIDs , with the following requirements: Has very low chance of collisions (to the point that we'd rather collide once a year than perform checks) Does not leak sensitive information, such as how many items exist Has high performance in an SQL database Is copy/pastable for manual querying (as both query string and query result) Is usable as a URI component without encoding To meet the requirements, I

问题 This question already has an answer here : What's with the integer cache maintained by the interpreter? (1 answer) Closed 5 years ago . Two individually created mutable list have different ids. Python SHELL: (mutable) >>> mylist = ['spam', 'eggs'] >>> yourlist = ['spam', 'eggs'] >>> id(mylist), id(yourlist) (49624456, 48910408) While two individually created immutable strings have similar ids. Python SHELL: (immutable) >>> a = 10 >>> b = 10 >>> id(a), id(b) (507099072, 507099072) Is a and b

问题 PHP allows Unicode identifiers for variables, functions, classes and constants anyhow. It was certainly intended for localized applications. Wether it's a good idea to code an API in anything but English is debatable, but it's undisputed that some development settings could demand it. $Schüssel = new Müsli(T_FRÜCHTE); But PHP allows more than just \p{L} for identifiers. You can use virtually any Unicode character, except those from the ASCII range (e.g. : is special or \ as that's already

问题 PHP allows Unicode identifiers for variables, functions, classes and constants anyhow. It was certainly intended for localized applications. Wether it's a good idea to code an API in anything but English is debatable, but it's undisputed that some development settings could demand it. $Schüssel = new Müsli(T_FRÜCHTE); But PHP allows more than just \p{L} for identifiers. You can use virtually any Unicode character, except those from the ASCII range (e.g. : is special or \ as that's already

问题 I need to generate a unique ID and was considering Guid.NewGuid to do this, which generates something of the form: 0fe66778-c4a8-4f93-9bda-366224df6f11 This is a little long for the string-type database column that it will end up residing in, so I was planning on truncating it. The question is: Is one end of a GUID more preferable than the rest in terms of uniqueness? Should I be lopping off the start, the end, or removing parts from the middle? Or does it just not matter? 回答1: You can save

问题 I'm building a spreadsheet app using MySQL as storage, I need to identify records that are being updated client-side in order to save the changes. Is there a way, such as some kind of "internal record identifier" (internal as in used by the database engine itself), to uniquely identify records, so that I'll be able to update the correct one? Certainly, a SELECT query can be used to identify the record, including all the fields in the table, but obviously that has the downside of returning

问题 Hope this question wasn't asked before. Does anyone know the character limit for domain names? For example if I write this: CREATE DOMAIN d_complement_activite_etablissement AS character varying it will create a domain with the name: d_complement_activite_etabliss (Yeah, I know how to count, but I want some more info on the subject). Is there a command that can change this maximum length? Is this length the same for other names (columns, tables etc)? 回答1: You ask: Is there a command that can

问题 I'm using hibernate with spring, h2 and liquibase and I'm trying to make a custom String id generator for my entities by taking example with this blog post but I'm getting an error : Caused by: org.hibernate.id.IdentifierGenerationException: Unknown integral data type for ids : java.lang.String Here my SequenceStyleGenerator code : public class CTCIDGenerator extends SequenceStyleGenerator { @Override public Serializable generate(SessionImplementor session, Object obj) { if (obj instanceof