Java Stream - 从 CSV 检索重复记录 [英] Java Stream - Retrieving repeated records from CSV

问题描述

我搜索了该网站并没有找到类似的内容.我是使用 Java 流的新手，但我知道它是循环命令的替代品.但是，我想知道是否有一种方法可以使用流过滤CSV文件，如下所示，结果中仅包含重复记录并按中心字段分组.

I searched the site and didn't find something similar. I'm newbie to using the Java stream, but I understand that it's a replacement for a loop command. However, I would like to know if there is a way to filter a CSV file using stream, as shown below, where only the repeated records are included in the result and grouped by the Center field.

初始 CSV 文件

最终结果

另外，同一对不能反向出现在最终结果中，如下表所示:

In addition, the same pair cannot appear in the final result inversely, as shown in the table below:

这不应该发生

有没有办法同时使用流和分组来做到这一点，因为理论上，执行任务需要两个循环?

Is there a way to do it using stream and grouping at the same time, since theoretically, two loops would be needed to perform the task?

提前致谢.

推荐答案

我从您的示例中了解到，如果除 ID 之外的所有属性都具有相同的值，您会将条目视为重复条目.您可以为此使用 anymatch:

What I understood from your examples is you consider an entry as duplicate if all the attributes have same value except the ID. You can use anymatch for this:

list.stream().filter(x ->
                list.stream().anyMatch(y -> isDuplicate(x, y))).collect(Collectors.toList())

那么 isDuplicate(x,y) 有什么作用?

这将返回一个 boolean.您可以在此方法中检查除 id 之外的所有条目是否具有相同的值:

This returns a boolean. You can check whether all the entries have same value except the id in this method:

private boolean isDuplicate(CsvEntry x, CsvEntry y) {
    return !x.getId().equals(y.getId())
            && x.getName().equals(y.getName())
            && x.getMother().equals(y.getMother())
            && x.getBirth().equals(y.getBirth());
}

我假设您已将所有条目视为 String.根据类型更改支票.这将为您提供具有相应 ID

I've assumed you've taken all the entries as String. Change the checks according to the type. This will give you the duplicate entries with their corresponding ID

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