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
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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