Get value for unique record using Pig - hadoop

Question

Below is the input data set.
col1,col2,col3,col4,col5
key1,111,1,12/11/2016,10
key2,111,1,12/11/2016,10
key3,111,1,12/11/2016,10
key4,222,2,12/22/2016,10
key5,222,2,12/22/2016,10
key6,333,3,12/30/2016,10
key7,111,0,12/11/2016,10
Based on col2,col3,col4 will give unique record, I need to get any one value from col1 for the unique record, and populate as new field say col6. The expected output below
col1,col2,col3,col4,col5,col6
key1,111,1,12/11/2016,10,key3
key2,111,1,12/11/2016,10,key3
key3,111,1,12/11/2016,10,key3
key4,222,2,12/22/2016,10,key5
key5,222,2,12/22/2016,10,key5
key6,333,3,12/30/2016,10,key6
key7,111,0,12/11/2016,10,key7
Below is the script, I am getting error.
A = load 'test1.csv' using PigStorage(',');
B = GROUP A by ($1,$2,$3);
C = FOREACH B GENERATE FLATTEN(group), MAX(A.$0);
ERROR org.apache.pig.tools.grunt.Grunt - ERROR 2106: Error executing an algebraic function

Answer 1

Looks like a good use case to use Nested Foreach
Ref : https://pig.apache.org/docs/r0.14.0/basic.html#foreach
Input :
key1,111,1,12/11/2016,10
key2,111,1,12/11/2016,10
key3,111,1,12/11/2016,10
key4,222,2,12/22/2016,10
key5,222,2,12/22/2016,10
key6,333,3,12/30/2016,10
key7,111,0,12/11/2016,10
PigScript
A = load 'input.csv' using PigStorage(',') AS (col1:chararray,col2:chararray,col3:chararray,col4:chararray,col5:chararray);
B = FOREACH(GROUP A BY (col2,col3,col4)) {
ordered = ORDER A BY col1 DESC;
latest = LIMIT ordered 1;
GENERATE FLATTEN(A) AS (col1:chararray,col2:chararray,col3:chararray,col4:chararray,col5:chararray), FLATTEN(latest.col1) AS col6:chararray;
};
DUMP B;
Output :
(key1,111,1,12/11/2016,10,key3)
(key2,111,1,12/11/2016,10,key3)
(key3,111,1,12/11/2016,10,key3)
(key4,222,2,12/22/2016,10,key5)
(key5,222,2,12/22/2016,10,key5)
(key6,333,3,12/30/2016,10,key6)
(key7,111,0,12/11/2016,10,key7)