将CSV文件合并到一个没有重复标题的文件中

Question

我有一些具有相同列标题的CSV文件。例如

文件A

header1,header2,header3
one,two,three
four,five,six

文件B

header1,header2,header3
seven,eight,nine
ten,eleven,twelve

我想合并它，以便将数据合并到一个文件中，标题在顶部，但其他地方没有标题。

header1,header2,header3
one,two,three
four,five,six
seven,eight,nine
ten,eleven,twelve

实现这一目标的好方法是什么？

Answer 1

在Java中这样做似乎有点重。它在Linux shell中非常简单：

(cat FileA ; tail --lines=+2 FileB) > FileC

Answer 2

下面是一个例子：

public static void main(String[] args) throws IOException {
    List<Path> paths = Arrays.asList(Paths.get("c:/temp/file1.csv"), Paths.get("c:/temp/file2.csv"));
    List<String> mergedLines = getMergedLines(paths);
    Path target = Paths.get("c:/temp/merged.csv");
    Files.write(target, mergedLines, Charset.forName("UTF-8"));
}

private static List<String> getMergedLines(List<Path> paths) throws IOException {
    List<String> mergedLines = new ArrayList<> ();
    for (Path p : paths){
        List<String> lines = Files.readAllLines(p, Charset.forName("UTF-8"));
        if (!lines.isEmpty()) {
            if (mergedLines.isEmpty()) {
                mergedLines.add(lines.get(0)); //add header only once
            }
            mergedLines.addAll(lines.subList(1, lines.size()));
        }
    }
    return mergedLines;
}

Answer 3

这应该行得通。它检查正在合并的文件是否有匹配的头。否则会抛出异常。异常处理（关闭流等）已留作练习。

String[] headers = null;
String firstFile = "/path/to/firstFile.dat";
Scanner scanner = new Scanner(new File(firstFile));

if (scanner.hasNextLine())
    headers[] = scanner.nextLine().split(",");

scanner.close();

Iterator<File> iterFiles = listOfFilesToBeMerged.iterator();
BufferedWriter writer = new BufferedWriter(new FileWriter(firstFile, true));

while (iterFiles.hasNext()) {
  File nextFile = iterFiles.next();
  BufferedReader reader = new BufferedReader(new FileReader(nextFile));

  String line = null;
  String[] firstLine = null;
  if ((line = reader.readLine()) != null)
    firstLine = line.split(",");

  if (!Arrays.equals (headers, firstLine))
    throw new FileMergeException("Header mis-match between CSV files: '" +
              firstFile + "' and '" + nextFile.getAbsolutePath());

  while ((line = reader.readLine()) != null) {
    writer.write(line);
    writer.newLine();
  }

  reader.close();
}
writer.close();