For the Map function:
Input key: default
input value: File A and File B lines
output key: A, B, C,....(first colomn of the final result)
output value: 12, 24, Car, 13, Van, SUV...
Reduce function:
take the Map output and do:
for each key
{ if the value of a key is integer
then same it to array1;
else save it to array2
}
for ith element in array1
for jth element in array2
output(key, array1[i]+"\t"+array2[j]);
done
Hope this helps.
On Mon, Apr 5, 2010 at 4:10 PM, M B <[email protected]> wrote:
> Hi, I need a good java example to get me started with some joining we need
> to do, any examples would be appreciated.
>
> File A:
> Field1 Field2
> A 12
> B 13
> C 22
> A 24
>
> File B:
> Field1 Field2 Field3
> A Car ...
> B Truck ...
> B SUV ...
> B Van ...
>
> So, we need to first join File A and B on Field1 (say both are string
> fields). The result would just be:
> A 12 Car ...
> A 24 Car ...
> B 13 Truck ...
> B 13 SUV ...
> B 13 Van ...
> and so on - with all the fields from both files returning.
>
> Once we have that, we sometimes need to then transform it so we have a
> single record per key (Field1):
> A (12,Car) (24,Car)
> B (13,Truck) (13,SUV) (13,Van)
> --however it looks, basically tuples for each key (we'll modify this later
> to return a conatenated set of fields from B, etc)
>
> At other times, instead of transforming to a single row, we just need to
> modify rows based on values. So if B.Field2 equals "Van", we need to set
> Output.Field2 = whatever then output to file ...
>
> Are there any good examples of this in native java (we can't use
> pig/hive/etc)?
>
> thanks.
>
--
Best Wishes！
－－
Chen He
PhD. student of CSE Dept.
Holland Computing Center
University of Nebraska-Lincoln
Lincoln NE 68588
