二维映射Java
我需要一个可以以二维方式存储信息的数据结构。例如，想象一个包含用户项目评级的表。我需要存储所有用户的所有评分。比方说，用户u1。我需要存储用户u1、u2和u3以及所有其他用户的评级。但问题是我还需要存储所有项目的所有评分。例如，我需要存储所有用户为每个项目提供的评分。所以我需要一个类似于地图的东西，对于用户来说，关键是用户ID，值是评级集。我很容易做到。但我的问题是如何存储物品的评级。例如，一个映射，其键是项目ID，值是用户为该项目提供的评分集。我想上传一个表，但因为我没有足够的声誉，所以我无法上传。所以想象一下，一个像二维矩阵一样的表，行是用户，列是项目。是否有一个数据结构可以做到这一点？或者我应该建立两个不同的地图？也许有一个比地图更好的选择，但因为我必须为我的问题选择一个标题，所以我写了地图二维映射Java,java,matrix,hashmap,Java,Matrix,Hashmap,我需要一个可以以二维方式存储信息的数据结构。例如，想象一个包含用户项目评级的表。我需要存储所有用户的所有评分。比方说，用户u1。我需要存储用户u1、u2和u3以及所有其他用户的评级。但问题是我还需要存储所有项目的所有评分。例如，我需要存储所有用户为每个项目提供的评分。所以我需要一个类似于地图的东西，对于用户来说，关键是用户ID，值是评级集。我很容易做到。但我的问题是如何存储物品的评级。例如，一个映射，其键是项目ID，值是用户为该项目提供的评分集。我想上传一个表，但因为我没有足够的声誉，所以我无法
谢谢所以，你有两个一个多的关系。一个用户有（给出）很多评分，一个项目有很多评分；这就产生了许多用户之间的关系，而这正是您的问题所在。为什么不简单地按照以下描述对其进行建模：
public class Rating {
private User ratedBy;
private Item itemRated;
public Item getItem() { return itemRated; }
}
public class User {
private Set<Rating> allRatings = new HashSet<>();
public Rating getRatingFor(Item item) {
for(Rating rating: allRatings) {
if(item.equals(rating.getItem()) {
return rating;
}
}
return null;
}
}
public class Item {
private Set<Rating> allRatings = new HashSet<>();
}
一个快速而肮脏的解决方案是使用二维键。 假设用户和项的id都是相同类型的，您可以创建一个类，该类只是id和密钥类型的持有者。（如果可用，类型可以是用户或项的类，也可以是枚举值）。然后使地图具有此类型的键。当然，每个等级至少会被引用两次（每种类型一次）您可以使用免费库中的类
Table Table=HashBasedTable.create（）；
表.put（1，“a”，2.0）；
双v=表。获取（1，“a”）；//获得2.0
guava表的API，以及您想要的实现，HashBasedTable，这里是我自己版本的适当表对象。请注意，使用现有库提供的东西是很好的。但是尝试自己的实现将帮助您更好地理解所涉及的问题。因此，您可以尝试将“删除”方法等添加到我的实现中以完成它 我更喜欢将数据保存在表中，而不是在
UserItemgetColgetRowequalshashCodepublic class Table<K1, K2, V> {
// Two maps allowing us to retrieve the value through the row or the
// column key.
private Map<K1, Map<K2, V>> rowMap;
private Map<K2, Map<K1, V>> colMap;
public Table() {
rowMap = new HashMap<>();
colMap = new HashMap<>();
}
/**
* Allows us to create a key for the row, and place it in the structure
* while there are still no relations for it.
*
* @param key
* The key for which a new empty row will be created.
*/
public void addEmptyRow(K1 key) {
if (!rowMap.containsKey(key)) {
rowMap.put(key, new HashMap<K2, V>());
}
}
/**
* Allows us to create a key for the column, and place it in the
* structure while there are still no relations for it.
*
* @param key
* The key for which a new empty column will be created.
*/
public void addEmptyCol(K2 key) {
if (!colMap.containsKey(key)) {
colMap.put(key, new HashMap<K1, V>());
}
}
/**
* Insert a value into the table using the two keys.
*
* @param rowKey
* Row key to access this value
* @param colKey
* Column key to access this value
* @param value
* The value to be associated with the above two keys.
*/
public void put(K1 rowKey, K2 colKey, V value) {
Map<K2, V> row;
Map<K1, V> col;
// Find the internal row. If there is no entry, create one.
if (rowMap.containsKey(rowKey)) {
row = rowMap.get(rowKey);
} else {
row = new HashMap<K2, V>();
rowMap.put(rowKey, row);
}
// Find the internal column, If there is no entry, create one.
if (colMap.containsKey(colKey)) {
col = colMap.get(colKey);
} else {
col = new HashMap<K1, V>();
colMap.put(colKey, col);
}
// Add the value to both row and column.
row.put(colKey, value);
col.put(rowKey, value);
}
/**
* Get the value associated with the given row and column.
*
* @param rowKey
* Row key to access the value
* @param colKey
* Column key to access the value
* @return Value in the given row and column. Null if mapping doesn't
* exist
*/
public V get(K1 rowKey, K2 colKey) {
Map<K2, V> row;
row = rowMap.get(rowKey);
if (row != null) {
return row.get(colKey);
}
return null;
}
/**
* Get a map representing the row for the given key. The map contains
* only column keys that actually have values in this row.
*
* @param rowKey
* The key to the row in the table
* @return Map representing the row. Null if there is no row with the
* given key.
*/
public Map<K2, V> getRow(K1 rowKey) {
// Note that we are returning a protective copy of the row. The user
// cannot change the internal structure of the table, but is allowed
// to change the value's state if it is mutable.
if (rowMap.containsKey(rowKey)) {
return new HashMap<>(rowMap.get(rowKey));
}
return null;
}
/**
* Get a map representing the column for the given key. The map contains
* only row keys that actually have values in this column.
*
* @param colKey
* The key to the column in the table.
* @return Map representing the column. Null if there is no column with
* the given key.
*/
public Map<K1, V> getCol(K2 colKey) {
// Note that we are returning a protective copy of the column. The
// user cannot change the internal structure.
if (colMap.containsKey(colKey)) {
return new HashMap<>(colMap.get(colKey));
}
return null;
}
/**
* Get a set of all the existing row keys.
*
* @return A Set containing all the row keys. The set may be empty.
*/
public Set<K1> getRowKeys() {
return new HashSet(rowMap.keySet());
}
/**
* Get a set of all the existing column keys.
*
* @return A set containing all the column keys. The set may be empty.
*/
public Set<K2> getColKeys() {
return new HashSet(colMap.keySet());
}
}
Map<Item, Rating> anakinsRatings = table.getRow(user);
for (Map.Entry<Item, Rating> entry : anakinsRatings.entrySet()) {
System.out.println(user + " rated " + entry.getKey() + " as "
+ entry.getValue().getRating());
}
Map anakinsrattings=table.getRow（用户）；
for（Map.Entry:anakinsRatings.entrySet（））{
System.out.println（用户+“额定值”+entry.getKey（）+“作为”
+entry.getValue（）.getRating（））；
}
for (Item currItem : table.getColKeys()) {
Map<User, Rating> itemMap = table.getCol(currItem);
if (itemMap.isEmpty()) {
System.out.println("There are currently no ratings for \""
+ currItem
+ "\"");
} else {
for (Map.Entry<User, Rating> entry : table.getCol(currItem).entrySet()) {
System.out.println("\""
+ currItem
+ "\" has been rated "
+ entry.getValue().getRating() + " by "
+ entry.getKey());
}
}
}
for（项curroitem:table.getColKeys（））{
Map itemMap=table.getCol（curroitem）；
if（itemMap.isEmpty（））{
System.out.println（“当前没有针对\”的评级”
+货币项目
+ "\"");
}否则{
for（Map.Entry:table.getCol（currItem.entrySet（））{
System.out.println（“\”）
+货币项目
+“\”已被评级”
+entry.getValue（）.getRating（）+“by”
+entry.getKey（））；
}
}
}
正如我所说的，实现还没有完成-表中没有
toStringremoveremoveowremoveColclear Table<User, Item, Rating> table = new Table<>();
table.addEmptyCol(new Item("Television"));
table.addEmptyCol(new Item("Sofa"));
User user = new User("Anakin");
Item item = new Item("Light Sabre");
table.put(user, item, new Rating(5));
Item item1 = new Item("Helmet");
table.put(user, item1, new Rating(7));
Rating rating = table.get(user, item);
rating.setRating(rating.getRating() + 10);
User user1 = new User("Obi-Wan");
table.put(user1, item, new Rating(8));
table.put(user1, new Item("Television"), new Rating(0));
Map<Item, Rating> anakinsRatings = table.getRow(user);
for (Map.Entry<Item, Rating> entry : anakinsRatings.entrySet()) {
System.out.println(user + " rated " + entry.getKey() + " as "
+ entry.getValue().getRating());
}
for (Item currItem : table.getColKeys()) {
Map<User, Rating> itemMap = table.getCol(currItem);
if (itemMap.isEmpty()) {
System.out.println("There are currently no ratings for \""
+ currItem
+ "\"");
} else {
for (Map.Entry<User, Rating> entry : table.getCol(currItem).entrySet()) {
System.out.println("\""
+ currItem
+ "\" has been rated "
+ entry.getValue().getRating() + " by "
+ entry.getKey());
}
}
}