unique

问题 My collection looks like this. var list = [{id:'12345', sequence:null}, {id:'12346', sequence:null}, {id:'12347', sequence:null}, {id:'12348', sequence:1}, {id:'12348', sequence:2}, {id:'12349', sequence:1}, {id:'12349', sequence:1}]; I am trying to get a unique list so that object with same id AND sequence will only return one of the objects (we have 2 here- {id:'12349', sequence:1}) my code var uniqueList = _.uniq(list, function(obj) { return obj.id && obj.sequence; }); can we use lodash

问题 My collection looks like this. var list = [{id:'12345', sequence:null}, {id:'12346', sequence:null}, {id:'12347', sequence:null}, {id:'12348', sequence:1}, {id:'12348', sequence:2}, {id:'12349', sequence:1}, {id:'12349', sequence:1}]; I am trying to get a unique list so that object with same id AND sequence will only return one of the objects (we have 2 here- {id:'12349', sequence:1}) my code var uniqueList = _.uniq(list, function(obj) { return obj.id && obj.sequence; }); can we use lodash

问题 I have a simple MySQL table with one column: name . I would like to define a unique constraint on this column. I can do: class MyModel < ActiveRecord::Base validates_uniqueness_of :my_column_name end but it will work only at the application level, not at the database level. What would you suggest ? 回答1: This is not super-helpful, but it looks like there is not a great answer for enforcing uniqueness at the database level. From the Rails migration guide: The Active Record way claims that

问题 I'm trying to generate a unique ID in php in order to store user-uploaded content on a FS without conflicts. I'm using php, and at the moment this little snippet is responsible for generating the UID: $id = tempnam (".", ""); unlink($id); $id = substr($id, 2); This code is hideous: it creates a temporary file on the FS and deletes it, retaining only the relevant unique part of the generated string. Is there any better way to do this, most preferably without any external dependencies? Thanks

问题 I have an application that saves data into a table called Jobs. The Jobs table has a column called Name which has a UNIQUE constraint. The Name column is not PRIMARY KEY. I wonder if I should check for duplicate entries myself before I try to save/update a new entry or if it's better to wait for an exception thrown by the data access layer. I'm using NHibernate for this App if it's of any importance Thanks to everybody for the great input. I have found one more reason why I should validate in

问题 I have in my MYSQL table a unique key and i want to add to it. UNIQUE KEY `user_id` (`user_id`,`account_id`) and i want to add another UNIQUE KEY `user_id` (`user_id`,`account_id`,`pet_id`) 回答1: ALTER TABLE your_table DROP INDEX user_id, ADD UNIQUE KEY `user_id` (`user_id`,`account_id`,`pet_id`) Note: You won't need the backticks around the column names if you're using mariadb on Linux - in fact it will throw an syntax error 1064/(42000) 回答2: Drop the first key and then create the new one. 来源

问题 I have the following situation. table looks like this CREATE TABLE CompetitionsLanguages ( competition REF CompetitionType SCOPE IS Competitions, language REF LanguageType SCOPE IS Languages ); I need this table to have a unique constraint on (competition,language) combination. oracle tells me that i cant put a UNIQUE or PK on columns that reference other tables. is it possible to somehow avoid the unique, using the CHECK, or some sort of a TRIGGER? 回答1: CREATE UNIQUE INDEX unqIndex ON

问题 Suppose I have a 100 x 100 matrix composed of some combination of 250s, 125s, 15s and 9s. I would like to return a sorted vector of all of the unique values in this matrix. Something in the matter of: sort(somefunction(matrix))=vector The result I would like to get is thus: vector=9,15,125,250 Is there a quick and easy way to do this? 回答1: b = unique(a) Check the docs on unique A = randi(9,10,10); unique(A) ans = 1 2 3 4 5 6 7 8 9 回答2: b = sort(a(:)); This should do the work sort your matrix;

问题 I have the following dataframe : df <- data.frame(Sl.No = c(1:6), Variable = c('a', 'a,b', 'a,b,c', 'b', 'c', 'b,c')) Sl.No Variable 1 a 2 a,b 3 a,b,c 4 b 5 c 6 b,c I want to separate the unique values in the variable column as list myList <- ("a", "b", "c") I have tried the following code: separator <- function(x) strsplit(x, ",")[[1]][[1]] unique(sapply(df$Variable, separator)) This however gives me the following output: "a" I request some help. I have searched but seem unable to find an

问题 For my dataframe, e.g. df = pd.DataFrame([1, 3, 7, 1], columns=['data']) I want to know for each index if the value is unique in the column data . So the resulting dataframe should be data is_unique 0 1 False 1 3 True 2 7 True 3 1 False Is there a convenient approach with pandas? 回答1: Use duplicated with invert mask by ~ : df['is_unique'] = ~df['data'].duplicated(keep=False) print (df) data is_unique 0 1 False 1 3 True 2 7 True 3 1 False 回答2: By using value_counts + map df.assign(BOOL=df.data