Pig latin search variabale name and min value - apache-pig

Question

I have a pig Latin question. I have a table with the following:
ID:Seller:Price:BID
1:John:20:B1
1:Ben:25:B1
2:John:60:B2
2:Chris:35:B2
3:John:20:B3
I'm able to group the table by ID using the following (assuming A is the LOAD table):
W = GROUP A BY ID;
But what I can't seem to figure out is the command to only return the values for the lowest price for each ID. In this example the final output should be:
1:John:20:B1
2:Chris:35:B2
3:John:20:B3
Cheers,
Shivedog

Answer 1

Generally you'll want to GROUP by the BID, then use MIN. However, since you want the whole tuple associated with the minimum value you'll want to use a UDF to do this.
myudfs.py
#outputSchema('vals: (ID: int, Seller: chararray, Price: chararray, BID: chararray)')
def get_min_tuple(bag):
return min(bag, key=lambda x: x[2])
myscript.pig
register 'myudfs.py' using jython as myudfs ;
-- A: (ID: int, Seller: chararray, Price: chararray, BID: chararray)
B = GROUP A BY BID ;
C = FOREACH B GENERATE group AS BID, FLATTEN(myudfs.get_min_tuple(A)) ;
-- Now you can do the JOIN to get the type of novel on C
Remember change the types (int,chararray,etc.) to the appropriate values.
Note: If multiple items in A have the same minimum price for an ID, then this will only return one of them.

Answer 2

option (1) - get all records with maximum price:
Use the new (Pig 0.11) RANK operator:
A = LOAD ...;
B = RANK A BY Price DESC;
C = FILTER B BY $0=1;
option (2) - get all records with maximum price:
Pig version below 0.11:
a = load ...;
b = group a by all;
c = foreach b generate MAX(a.price) as maxprice;
d = JOIN a BY price, c BY maxprice;
option (3) - use org.apache.pig.piggybank.evaluation.ExtremalTupleByNthField to get one of the tuples with maximum price:
define mMax org.apache.pig.piggybank.evaluation.ExtremalTupleByNthField( '4', 'max' );
a = load ...;
b = group a by all;
c - foreach b generate mMax(a);