找到两个列表中的所有共同元素

huangapple
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英文:

Find all common elements in two lists

问题

我正试图找出我的 ArrayList "list1" 中的共同元素。

  1. List<LocalDate> list1 = new ArrayList<> ();
  2. for (LocalDate d = dateFrom; !d.isAfter(dateTo); d = d.plusDays(1)) {
  3.     dates.add(d);

其中包含了从 "dateFrom" 到 "dateTo" 之间的所有日期，以及我的列表 "list2"。

  1. List<LocalDate> list2 = Arrays.asList(dateTime);

其中 dateTime 是一个变量，仅存储来自具有以下结构的文本文件的日期：

  1. 1946-01-12;07:00:00;-1.3;G
  2. 1946-01-12;13:00:00;0.3;G
  3. 1946-01-12;18:00:00;-2.8;G
  4. 1946-01-13;07:00:00;-6.2;G
  5. 1946-01-13;13:00:00;-4.7;G
  6. 1946-01-13;18:00:00;-4.3;G

我尝试使用 list2.retainAll(list1); 来查找列表2中也在列表1中的所有日期，但我认为问题在于列表2不是 ArrayList。我该如何修复这个问题？

  1. private static List<WeatherDataHandler> weatherData = new ArrayList<>();
  2. public void loadData(String filePath) throws IOException {
  3. // 读取所有数据
  4.     List<String> fileData = Files.readAllLines(Paths.get("filePath"));
  6.     Map<String, Long> frequencyMap = new LinkedHashMap<>();
  7.     
  8.     LocalDate dateFrom = LocalDate.of(1946, 01, 12);
  9.     LocalDate dateTo = LocalDate.of(1946, 01, 14);
  11.     List<LocalDate> list1 = new ArrayList<>();
  12.     for (LocalDate d = dateFrom; !d.isAfter(dateTo); d = d.plusDays(1)) {
  13.         dates.add(d);
  14.     }
  16.     for (String str : fileData) {
  17.         List<String> parsed = parseData(str);
  18.         LocalDate dateTime = LocalDate.parse(parsed.get(0));
  19.         LocalTime Time = LocalTime.parse(parsed.get(1));
  20.         double temperature = Double.parseDouble(parsed.get(2));
  21.         String tag = parsed.get(3);
  23.         WeatherDataHandler weather = new WeatherDataHandler(dateTime, Time, temperature, tag);
  24.         weatherData.add(weather);
  26.         List<LocalDate> list2 = Arrays.asList(dateTime);
  28.         list2.retainAll(list1); 
  29.         
  30.         String strDate = list2.toString();
  31.         frequencyMap.compute(strDate,
  32.                 (date, count) -> count == null ? 1 : count + 1);
  33.     }
  35.     for (Map.Entry<String, Long> entry : frequencyMap.entrySet()) {
  36.         if (entry.getValue() < 24) {
  37.             System.out.println(
  38.                     entry.getKey() + ": " + (24 - entry.getValue()));
  39.         }
  40.     }
  41. }
英文:

I am trying to find the common elements in my ArrayList "list1"

  1. List&lt;LocalDate&gt; list1 = new ArrayList&lt;&gt; ();
  2. for (LocalDate d = dateFrom; !d.isAfter(dateTo); d = d.plusDays(1)) {
  3.       dates.add(d);

that consists of all dates between "dateFrom" and "dateTo" and my list "list2"

  1. List&lt;LocalDate&gt; list2 = Arrays.asList(dateTime);

where dateTime is a variable that stores only the dates from a textfile with the following structure:

  1. 1946-01-12;07:00:00;-1.3;G
  2. 1946-01-12;13:00:00;0.3;G
  3. 1946-01-12;18:00:00;-2.8;G
  4. 1946-01-13;07:00:00;-6.2;G
  5. 1946-01-13;13:00:00;-4.7;G
  6. 1946-01-13;18:00:00;-4.3;G

I tried using list2.retainAll(list1); in order to find all the dates in list2 that is also in list1, but I think my problem is that list2 is not an arraylist. How can I fix that?

  1. private static List&lt;WeatherDataHandler&gt; weatherData = new ArrayList&lt;&gt;();
  2. public void loadData(String filePath) throws IOException {
  3. //Read all data
  4. 	List&lt;String&gt; fileData = Files.readAllLines(Paths.get(&quot;filePath&quot;));
  6. 	Map&lt;String, Long&gt; frequencyMap = new LinkedHashMap&lt;&gt;();
  7. 	
  8. 	LocalDate dateFrom = LocalDate.of(1946,01,12);
  9. 	LocalDate dateTo = LocalDate.of(1946, 01, 14);
  11.     List&lt;LocalDate&gt; list1 = new ArrayList&lt;&gt; ();
  12.     for (LocalDate d = dateFrom; !d.isAfter(dateTo); d = d.plusDays(1)) {
  13.       dates.add(d);
  14.      
  15.     }
  17.     for(String str : fileData) {
  18.         List&lt;String&gt; parsed = parseData(str);
  19.         LocalDate dateTime = LocalDate.parse(parsed.get(0));
  20.         LocalTime Time = LocalTime.parse(parsed.get(1));
  21.         double temperature = Double.parseDouble(parsed.get(2));
  22.         String tag = parsed.get(3);
  24.         WeatherDataHandler weather = new WeatherDataHandler(dateTime, Time, temperature, tag);
  25.         weatherData.add(weather);
  27.         List&lt;LocalDate&gt; list2 = Arrays.asList(dateTime);
  29.         list2.retainAll(list1); 
  30.         
  31.         String strDate = list2.toString();
  32.         frequencyMap.compute(strDate,
  33.                 (date, count) -&gt; count == null ? 1 : count + 1);
  34.     }
  36.     for (Map.Entry&lt;String, Long&gt; entry : frequencyMap
  37.             .entrySet()) {
  38.     	if (entry.getValue() &lt; 24){
  39.         System.out.println(
  40.                 entry.getKey() + &quot;: &quot; + (24-entry.getValue()));
  41.     }}

答案1

得分: 0

你可以按照以下方式进行操作：

  1. List<LocalDate> commonList = new ArrayList<LocalDate>();
  2. for (LocalDate date : list1) {
  3.     if(list2.contains(date)) {
  4.         commonList.add(date);
  5.     }
  6. }
  7. System.out.println("Common elements: " + commonList);

[更新]

在你的代码中将

  1. if (entry.getValue() < 24)

替换为

  1. if (entry.getValue() < 24 && !entry.getKey().equals("[]"))

以消除类似 []: 23 的内容。

英文:

You can do it as follows:

  1. List&lt;LocalDate&gt; commonList = new ArrayList&lt;LocalDate&gt;();
  2. for (LocalDate date : list1) {
  3. 	if(list2.contains(date)) {
  4. 		commonList.add(date);
  5. 	}
  6. }
  7. System.out.println(&quot;Common elements: &quot; + commonList)

[Update]

Replace

  1. if (entry.getValue() &lt; 24)

with

  1. if (entry.getValue() &lt; 24 &amp;&amp; !entry.getKey().equals(&quot;[]&quot;))

in your code to get rid of something like []: 23.

huangapple
  • 本文由 发表于 2020年3月4日 03:41:15
  • 转载请务必保留本文链接：https://go.coder-hub.com/60514392.html
  • arraylist
  • date
  • java
  • list
  • string
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