javacsvjava-stream

Retrieving repeated records from a CSV using the Java Stream API

I'm a 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.

Initial CSV file

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Final result

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

This shouldn't happen

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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?

Solution

  • 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())

    So what does the isDuplicate(x,y) do?

    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());
}

    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