multi-mapping | 易学教程

Report on a multimap by producing a new map of each key mapped to the count of elements in its collection value

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问题 Imagine a multimap tracking persons, each of whom has a list of assigned tasks. Map< Person , List< Task > > personToTasks = Map.of( new Person( "Alice" ) , List.of( new Task( "a1" ), new Task( "a2") ) , new Person( "Bob" ) , List.of( new Task( "b1" ) ) , new Person( "Carol" ) , List.of( new Task( "c1" ), new Task( "c2"), new Task( "c3") ) ) ; How can I use streams to get a new map, mapping each Person to an Integer with the count of items found in their list of assigned tasks? How to get a

Report on a multimap by producing a new map of each key mapped to the count of elements in its collection value

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Invert a Map with redundant values to produce a multimap

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问题 Given a map such as this where we have a frequency count per day-of-week for a year: Map.of( DayOfWeek.MONDAY , 52 , DayOfWeek.TUESDAY , 52 , DayOfWeek.WEDNESDAY, 53 , DayOfWeek.THURSDAY , 53 , DayOfWeek.FRIDAY , 52 , DayOfWeek.SATURDAY , 52 , DayOfWeek.SUNDAY , 52 ) …or as text: {MONDAY=52, TUESDAY=52, WEDNESDAY=53, THURSDAY=53, FRIDAY=52, SATURDAY=52, SUNDAY=52} …how can I invert to produce a multimap of distinct numbers each leading to a collection (list? set?) of the DayOfWeek which owned

Invert a Map with redundant values to produce a multimap

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How to achieve this Map<String, List<>> structure [closed]

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问题 Closed. This question is off-topic. It is not currently accepting answers. Want to improve this question? Update the question so it's on-topic for Stack Overflow. Closed 6 years ago . I have data like below: Key value ----- ------ car toyota car bmw car honda fruit apple fruit banana computer acer computer asus computer ibm ... (Each row of above data is an object with fields "key" and "value", all in one List List<DataObject> ) I would like to construct the data to a Map<String, List<String>

Multi-Mapper to create object hierarchy

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问题 I've been playing around with this for a bit, because it seems like it feels a lot like the documented posts/users example, but its slightly different and isn't working for me. Assuming the following simplified setup (a contact has multiple phone numbers): public class Contact { public int ContactID { get; set; } public string ContactName { get; set; } public IEnumerable<Phone> Phones { get; set; } } public class Phone { public int PhoneId { get; set; } public int ContactID { get; set; } //

How do I return one-to-many records in a specific order with Dapper and multi-mapping?

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问题 From Github: Dapper allows you to map a single row to multiple objects. This is a key feature if you want to avoid extraneous querying and eager load associations. Example: Consider 2 classes: Post and User > class Post { > public int Id { get; set; } > public string Title { get; set; } > public string Content { get; set; } > public User Owner { get; set; } } > > class User { > public int Id { get; set; } > public string Name { get; set; } } Now let us say that we want to map a query that

How to achieve this Map<String, List<>> structure [closed]

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Closed. This question is off-topic. It is not currently accepting answers. Learn more . Want to improve this question? Update the question so it's on-topic for Stack Overflow. I have data like below: Key value ----- ------ car toyota car bmw car honda fruit apple fruit banana computer acer computer asus computer ibm ... (Each row of above data is an object with fields "key" and "value", all in one List List<DataObject> ) I would like to construct the data to a Map<String, List<String>> like following: "car" : ["toyota", "bmw", "honda"] "fruit" : ["apple","banana"] "computer" : ["acer","asus",

Can't get multi-mapping to work in Dapper

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问题 Playing around with Dapper, I'm quite pleased with the results so far - intriguing! But now, my next scenario would be to read data from two tables - a Student and an Address table. Student table has a primary key of StudentID (INT IDENTITY) , Address has an AddressID (INT IDENTITY) . Student also has an FK called AddressID linking into the Address table. My idea was to create two classes, one for each table, with the properties I'm interested in. Additionally, I put an PrimaryAddress

Multi-Mapper to create object hierarchy

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I've been playing around with this for a bit, because it seems like it feels a lot like the documented posts/users example , but its slightly different and isn't working for me. Assuming the following simplified setup (a contact has multiple phone numbers): public class Contact { public int ContactID { get; set; } public string ContactName { get; set; } public IEnumerable<Phone> Phones { get; set; } } public class Phone { public int PhoneId { get; set; } public int ContactID { get; set; } // foreign key public string Number { get; set; } public string Type { get; set; } public bool IsActive {