我正在尝试处理以下数据：

B = FOREACH A GENERATE FLATTEN( vitalStatus);
DUMB B;
(value,LIVING)
(value,LIVING)
(value,LIVING)
(value,DECEASED)
(value,LIVING)
(value,DECEASED)
(value,DECEASED)
(value,LIVING)

但是，当我试图过滤它时（按vitalstatus匹配‘已故’的过滤器a），我做错了什么？
我得到以下错误：

2013-08-23 08:47:16,290 [Thread-4] WARN  org.apache.hadoop.mapred.LocalJobRunner - job_local_0001
java.lang.ClassCastException: org.apache.pig.data.BinSedesTuple cannot be cast to java.lang.String
    at org.apache.pig.backend.hadoop.executionengine.physicalLayer.expressionOperators.PORegexp.getNext(PORegexp.java:84)
    at org.apache.pig.backend.hadoop.executionengine.physicalLayer.relationalOperators.POFilter.getNext(POFilter.java:148)
    at org.apache.pig.backend.hadoop.executionengine.physicalLayer.PhysicalOperator.processInput(PhysicalOperator.java:290)
    at org.apache.pig.backend.hadoop.executionengine.physicalLayer.relationalOperators.POForEach.getNext(POForEach.java:233)
    at org.apache.pig.backend.hadoop.executionengine.mapReduceLayer.PigGenericMapReduce$Reduce.runPipeline(PigGenericMapReduce.java:460)
...