在 Map reduce java 中跳过 .csv 的第一行

问题描述

由于 mapper 函数对每一行都运行，我可以知道如何跳过第一行吗?对于某些文件，它包含我想忽略的列标题

As mapper function runs for every line , can i know the way how to skip the first line. For some file it consists of column header which i want to ignore

推荐答案

在mapper中读取文件时，数据以键值对的形式读入.关键是下一行开始的字节偏移量.对于第 1 行，它始终为零.所以在映射器函数中执行以下操作

In mapper while reading the file, the data is read in as key-value pair. The key is the byte offset where the next line starts. For line 1 it is always zero. So in mapper function do the following

    @Override
    public void map(LongWritable key, Text value, Context context) throws IOException {
        try {
            if (key.get() == 0 && value.toString().contains("header") /*Some condition satisfying it is header*/)
                return;
            else {
                // For rest of data it goes here
            }
        } catch (Exception e) {
            e.printStackTrace();
        }
    }     

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