MapReduce之气象数据分析MapReduce之气象数据分析

MapReduce之气象数据分析

问题描述

通过获取的气象数据来分析气温最大值

样例输入

数据集地址： 天气数据集

样例输出

表示1901年最大温度为239，可能是他们使用的温度单位和咱们不一样吧

mapper阶段任务

map阶段主要是对文本进行切割，提取时间和温度形成 <时间，<温度，，温度，温度>>的键值对

mapper阶段编码如下

    public static class MaxTemperatureMapper extends Mapper{
            private static final int MISSING=9999;
            public void map(LongWritable key,Text value,Context context) throws IOException,InterruptedException{
                String line=value.toString();
                String year=line.substring(15,19);
                int airTemperature;
                if(line.charAt(87)=='+'){
                    airTemperature=Integer.parseInt(line.substring(88,92));
                }else{
                    airTemperature=Integer.parseInt(line.substring(87,92));
                }
                String quality=line.substring(92,93);
                if(airTemperature!=MISSING&&quality.matches("[01459]")){
                    context.write(new Text(year),new IntWritable(airTemperature));
                }
            }
        }

reducer阶段任务

reduce阶段任务就是从<时间，<温度，温度>>中遍历温度并查找的最大值

reducer阶段编码如下

    public static class MaxTemperatureReducer extends Reducer{
            public void reduce(Text key, Iterable values,Context context) throws IOException,InterruptedException{
                int maxValue=Integer.MIN_VALUE;
                for (IntWritable value : values) {
                    maxValue = Math.max(maxValue, value.get());
                }
                context.write(key,new IntWritable(maxValue));
            }
        }

完整代码如下

    import org.apache.hadoop.conf.Configuration;
    import org.apache.hadoop.fs.Path;
    import org.apache.hadoop.io.IntWritable;
    import org.apache.hadoop.io.LongWritable;
    import org.apache.hadoop.io.Text;
    import org.apache.hadoop.mapreduce.Job;
    import org.apache.hadoop.mapreduce.Mapper;
    import org.apache.hadoop.mapreduce.Reducer;
    import org.apache.hadoop.mapreduce.lib.input.FileInputFormat;
    import org.apache.hadoop.mapreduce.lib.output.FileOutputFormat;
    import java.io.IOException;
    import java.lang.InterruptedException;
    import java.util.Iterator;
    
    public class Ncdc {
        public static class MaxTemperatureMapper extends Mapper{
            private static final int MISSING=9999;
            public void map(LongWritable key,Text value,Context context) throws IOException,InterruptedException{
                String line=value.toString();
                String year=line.substring(15,19);    //获取时间，可以修改成月和日
                int airTemperature;    //获取温度
                if(line.charAt(87)=='+'){
                    airTemperature=Integer.parseInt(line.substring(88,92));
                }else{
                    airTemperature=Integer.parseInt(line.substring(87,92));
                }
                String quality=line.substring(92,93);
                if(airTemperature!=MISSING&&quality.matches("[01459]")){
                    context.write(new Text(year),new IntWritable(airTemperature));
                }
            }
        }
        public static class MaxTemperatureReducer extends Reducer{
            public void reduce(Text key, Iterable values,Context context) throws IOException,InterruptedException{
                int maxValue=Integer.MIN_VALUE;  //遍历查找最大值
                for (IntWritable value : values) {
                    maxValue = Math.max(maxValue, value.get());
                }
                context.write(key,new IntWritable(maxValue));
            }
        }
        public static void main(String[] args) throws Exception{
            Configuration conf=new Configuration();
            String[] otherArgs=new String[]{"input/file.txt","output"};
            if(otherArgs.length!=2){
                System.err.println("参数错误");
                System.exit(2);
            }
            Job job= new Job(conf,"Ncdsc");
            FileInputFormat.addInputPath(job,new Path(otherArgs[0]));
            FileOutputFormat.setOutputPath(job,new Path(otherArgs[1]));
            job.setJarByClass(Ncdc.class);
            job.setMapperClass(MaxTemperatureMapper.class);
            job.setReducerClass(MaxTemperatureReducer.class);
            job.setOutputKeyClass(Text.class);
            job.setOutputValueClass(IntWritable.class);
            System.exit(job.waitForCompletion(true)?0:1);
        }
    }

写在最后

这段程序既可以以年为单位查找最大气温，还可以以月，日为单位，有兴趣大家可以自行修改map阶段中的相关代码