unique

问题 I have an object with a String that holds a unique id . (such as "ocx7gf" or "67hfs8") I need to supply it an implementation of int hascode() which will be unique obviously. how do i cast a string to a unique int in the easiest/fastest way? 10x. Edit - OK. I already know that String.hashcode is possible. But it is not recommended in any place. Actually' if any other method is not recommended - Should I use it or not if I have my object in a collection and I need the hashcode. should I concat

问题 Let's say I have following model structure: @Entity @Table(....) public class AnnotationGroup{ ... private List<AnnotationOption> options; @OneToMany(cascade = CascadeType.ALL, fetch = FetchType.EAGER, orphanRemoval = true) @JoinColumn(name = "annotation_group_id", nullable = false) public List<AnnotationOption> getOptions() { return options; } } @Entity @Table(...) public class AnnotationOption { private Long id; @Id @GeneratedValue(strategy = GenerationType.IDENTITY) @Override public Long

问题 I'd like to subset a dataframe to include only rows that have unique combinations of three columns. My situation is similar to the one presented in this question, but I'd like to preserve the other columns in my data as well. Here's my example: > df v1 v2 v3 v4 v5 1 7 1 A 100 98 2 7 2 A 98 97 3 8 1 C NA 80 4 8 1 C 78 75 5 8 1 C 50 62 6 9 3 C 75 75 The requested output would be something like this, where I'm looking for unique cases based on v1, v2, and v3 only: > df.new v1 v2 v3 v4 v5 1 7 1 A

问题 I am confused if in MySQL unique constraint is physical index or virtual index? And as unique constraint is defined on a column then, Is there any need to make a hash column also and defining index on hash column to speed up the process of queries considering that unique constraint column contains variable number of characters mostly above 40 characters and on average 50+? And total records are 150+ million plus. I have asked another question with details of hashes and its indexing plan.

问题 Say I have one column called colors with 1000 cells populated with values. Some of the cells have the word blue in it. In another column I have unique identifiers that correspond with the colors column. For example Blue can have a value associated to it of 01, 02, 04, or 05. The word blue appears 20 times within my name column. What is one way I can find how many unique identifiers are associated with the word blue ? In the example listed above the answer should return 4. The current method I

问题 Using XSLT 2.0 and Apache FOP I want to be able to create a new variable, have unique and sorted values inside it by category but preserve the nodes. So the new variable should have the following nodes: <category>1. First Aid</category> <category>2. Access control</category> <category>3. Fire safety</category> <category>4. Recognition</category> The input XML is the following: <equipment> <E0132> <category>1. First Aid</category> <description>Lorem ipsum dolor sit amet, consectetur adipiscing

问题 I am currently using django-registration v0.8a and django-recaptcha for my registration portion. Everything is working fine with the recaptcha field showing up except that I am unable to get the RegistrationFormUniqueEmail to work. Here are some of the details. I have ensured that my captcha\forms.py is indeed subclassing from the correct form: from registration.forms import RegistrationFormUniqueEmail class RegistrationFormCaptcha(RegistrationFormUniqueEmail): captcha = ReCaptchaField(attrs=

问题 I try to count the unique values in list but they have to fulfill the condition I have set. {=SUM(IF($A$1:$A$25=$D$2; 1/COUNTIF($B$1:$B$25; $B$1:$B$25); 0))} There the first 25 rows of the data as example. How to count unique distinct values if condition is true in Excel? 回答1: Just will posting the question, I found the answer: {=SUM(IF($D$1=$A$1:$D$25, 1/(COUNTIFS($A$1:$A$25; $D$2; $B$1:$E$25; $B$1:$B$25)); 0))} 来源： https://stackoverflow.com/questions/33213119/count-unique-distinct-values-if

问题 I have a table inquiry with columns job , gender ( TRUE for women, FALSE for men) and salary . None of the columns is unique, salary may contain NULL . How to find the minimum salary per job for women ( TRUE )? If e.g. there are entries [pilot ; TRUE ; 100] , [pilot ; FALSE ; 100] , [pilot ; TRUE ; NULL] and [pilot ; FALSE ; 120] , the code below returns [pilot ; 100] twice instead of once. SELECT TOP (100) PERCENT T.JOB, T.SALARY FROM INQUIRY AS T INNER JOIN (SELECT JOB, MIN(SALARY) AS SL

问题 This question already has an answer here : Select equivalent rows [A-B & B-A] [duplicate] (1 answer) Closed 3 years ago . I have a data frame with 1000 observations on 20 variables. I want to select only the rows that have a unique combination across columns, regardless of their order. That is, if a combination is ABA and another is BAA , I want the code only to return one of these combinations. To identify unique combinations I run a simple unique command across multiple variables. How would