java (mapreduce)

1. Implementation of java mapreduce

 

data block

1950,0

1950,22

1950,-11

1949,111

1949,78

For example: (1950,0),(1950,22),(1950,-11),(1949,111),(1949,78) Find the maximum value for each year

 

Fake code

map function

public void map(LongWritable key,Text value,Context context)

{

           String line = value.toStirng();

           

            context.write(year,value)

}

 

reduce function

pubilc void reduce(Text key,values,context){

year = key                 

for (value :values){

                         maxvalue= max(value)

                  } 

 context.write(year,maxvalue) returns the maximum value for each year

}

 

main method

new job

 map.class

reduce.class