为什么 Apache commons csv 解析器将唯一数据附加到第二个结果集中？

Question

我在一个目录中有 2 个 CSV 文件（district1.csv、district2.csv），每个文件包含一列 schoolCode。当我使用 Apache commons CSV 库读取两个 CSV 文件时，我正在读取 schoolCode 列的不同值并计算结果。这是我的代码：

public void getDistinctRecordCount() throws IOException {
        Set<String> uniqueSchools = new HashSet<>();
        int numOfSchools;
        String SchoolCode;

    //Filter to only read csv files.
    File[] files = Directory.listFiles(new FileExtensionFilter());

    for (File f : files) {
        CSVParser csvParser;
        CSVFormat csvFormat = CSVFormat.DEFAULT.withFirstRecordAsHeader().withIgnoreHeaderCase().withTrim();
        reader = Files.newBufferedReader(Paths.get(Directory + "\" + f.getName() ), StandardCharsets.ISO_8859_1);
        csvParser = CSVParser.parse(reader, csvFormat);
        for (CSVRecord column : csvParser) {
            SchoolCode = column.get("School Code");
            uniqueSchools.add(SchoolCode);
        }
        Logger.info("The list of Schools for " + f.getName() + " are: " + uniqueSchools);
        numOfSchools = uniqueSchools.size();
        Logger.info("The total count of Schools for " + f.getName() + " are: " + numOfSchools);
        Logger.info("-----------------------");
    }
}

这是我的输出：

[INFO ] [Logger] - The list of Schools for district1.csv are: [01-0003-002, 01-0003-001]
[INFO ] [Logger] - The total count of Schools for district1.csv are: 2
[INFO ] [Logger] - The list of Schools for district2.csv are: [01-0003-002, 01-0003-001, 01-0018-004, 01-0018-005, 01-0018-002, 01-0018-003, 01-0018-008, 01-0018-006]
[INFO ] [Logger] - The total count of Schools for district2.csv are: 8

问题：从 district1.csv 结果中读入的两个值附加到 district2.csv 结果，使我对 district2.csv 的计数减去 2（实际正确值应该是 6 ).它是如何附加的？

Answer 1

如果您不需要所有学校的集合，您可以将 uniqueSchools 移动到循环内或 clear 它：

for (File f : files) {
   uniqueSchools.clear();

您还可以在 Map<String, String> 中保存每个文件的学校或为每个文件创建一组，记录计数，然后 addAll 设置为 uniqueSchools

Set<String> currentSchools = new HashSet<>();
..
currentSchools.add(SchoolCode);
Logger.info("The list of Schools for " + f.getName() + " are: " + currentSchools);
numOfSchools = currentSchools.size();
Logger.info("The total count of Schools for " + f.getName() + " are: " + numOfSchools);        
uniqueSchools.addAll(currentSchools);

考虑小写（驼峰式）变量的首字母，例如将 SchoolCode 更改为 schoolCode 并将 Logger 更改为 logger

为什么 Apache commons csv 解析器将唯一数据附加到第二个结果集中？

Why is Apache commons csv parser appending unique data into 2nd result set?

java

csv

set

apache-commons-csv