反转键/值 - 创建HashMap的新实例 [英] reversing keys/values - create new instance of HashMap

问题描述

我有一个现存的HashMap实例，简称为sale （它是Map< String，Set< String>>）我用它来记录客户和项目历史。

有没有办法创建一个新的HashMap实例，这有效地反转了这种用法？即将每件物品作为一个唯一的钥匙购买，并将相应的价值显示为购买该产品的顾客的字符串集合。我怀疑有一个简单的过程使用keySet（）以某种方式迭代销售映射，但我无法看到如何执行此操作。
任何帮助将不胜感激。

解决方案

你的意思是你想要一些像Map，String>的东西！

您可以迭代现有地图并将反转键值放入新地图中。例如： p>

 映射< Set< String>，String> somemap = new HashMap< Set< String>，String>（）; 
 foreach（Map.entry entry：existingMap.entrySet（））{
 Set< String> value = entry.getValue（）; 
 String key = entry.getKey（）; 
 somemap.put（value，key）; 
 
} 
  

I’ve got an existing instance of HashMap simply called sale (it is Map<String, Set<String>>) I use it to log customers and items history.

Is there a way to create a new instance of HashMap, that effectively reverses this usage? i.e will show each item purchased as a unique key and the corresponding value as a String set of the customers that have purchased that product. I suspect there is a simple process using keySet() in some way to iterate over the sales map but I just can’t see how to do this. Any help would be much appreciated.

解决方案

do you mean you want some thing like Map, String> !!

Thn you can iterate over existing map and put reversed key values in a new map

Example:

Map<Set<String>, String> somemap = new HashMap<Set<String>, String>();
foreach(Map.entry entry : existingMap.entrySet()) {
  Set<String> value = entry.getValue();
  String key = entry.getKey();
  somemap.put(value,key);

}

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