One way to unfold tuples and create multiple tuples, each containing one field:
$ cat data.txt
val1a,val2a,val3a,val4a,val5a,val6a,val7a
val1b,val2b,val3b
val1c,val2c
A = load 'data.txt' using PigStorage(',');
B = foreach A generate FLATTEN(TOBAG(*));
dump B;
(val1a)
(val2a)
(val3a)
(val4a)
(val5a)
(val6a)
(val7a)
(val1b)
(val2b)
(val3b)
(val1c)
(val2c)
Note:
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