计算Hashmap中的重复值 [英] Counting duplicate values in Hashmap

问题描述

我有一个看起来像这样的哈希映射:

HashMap>varX = new HashMap>();

而且我一生都无法计算出如何计算重复值的数量.例如，如果 put("001", "DM"); 进入哈希映射，put("010", "DM"); 以及，如何如果 Hashmap 的 ArrayList 部分中有两个值，则计数.

例如，输出看起来像这样:

DM:2 因为我将两个 DM 值放入"了 Hashmap.

解决方案

您有一个 HashMap 将 String 映射到 ArrayList.

在这张地图上执行 put("001", "DM") 将不会像 @Sotirios Delimanolis 在评论中指出的那样工作.

你会得到如下错误:

方法 put(String, ArrayList) 在类型 HashMap>不适用于参数 (String, String)

根据您的示例行为，您需要一个 HashMap 将 String 映射到 String(即 put("001","DM");

现在，假设你有:

HashMapvarX = new HashMap();

并且您想计算有多少键映射到相同的值，您可以这样做:

varX.put("001", "DM");varX.put("010", "DM");//...整数计数器 = 0;字符串计数For = "DM";for(String key : varX.keySet()) {//遍历这个 HashMap 中的所有键if(varX.get(key).equals(countingFor)) {//如果一个键映射到你需要的字符串，增加计数器计数器++；}}System.out.println(countingFor + ":" + counter);//将打印出DM:2"

I have a hash map that looks like this:

HashMap<String, ArrayList<String>> varX = new HashMap<String, ArrayList<String>>();

And I can't for the life of me work out how to count the number of duplicate values. For example, If put("001", "DM"); into the hash map and put("010", "DM"); as well, how can count if there are two values int the ArrayList section of the Hashmap.

For example, the output would look something like this:

DM:2 as I 'put' two DM values into the Hashmap.

解决方案

You have a HashMap that maps String to ArrayList<String>.

Doing put("001", "DM") on this map will not work as was pointed out to you in the comments by @Sotirios Delimanolis.

You would get an error that looks like:

The method put(String, ArrayList<String>) in the type HashMap<String,ArrayList<String>> is not applicable for the arguments (String, String)

Based on your example behavior, you want a HashMap that maps String to String (i.e. put("001", "DM");

Now, assuming you have that:

HashMap<String, String> varX = new HashMap<String, String>();

And you want to count how many keys map to the same value, here's how you can do that:

varX.put("001", "DM");
varX.put("010", "DM");

// ...

int counter = 0;
String countingFor = "DM";
for(String key : varX.keySet()) {            // iterate through all the keys in this HashMap
    if(varX.get(key).equals(countingFor)) {  // if a key maps to the string you need, increment the counter
        counter++;
    }
}
System.out.println(countingFor + ":" + counter);  // would print out "DM:2"

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