This class implements a mapper/reducer class that can be used to perform
 * field selections in a manner similar to unix cut. The input data is treated
 * as fields separated by a user specified separator (the default value is
 * "\t"). The user can specify a list of fields that form the map output keys,
 * and a list of fields that form the map output values. If the inputformat is
 * TextInputFormat, the mapper will ignore the key to the map function. and the
 * fields are from the value only. Otherwise, the fields are the union of those
 * from the key and those from the value.
This class implements a mapper/reducer class that can be used to perform
 * field selections in a manner similar to unix cut. The input data is treated
 * as fields separated by a user specified separator (the default value is
 * "\t"). The user can specify a list of fields that form the map output keys,
 * and a list of fields that form the map output values. If the inputformat is
 * TextInputFormat, the mapper will ignore the key to the map function. and the
 * fields are from the value only. Otherwise, the fields are the union of those
 * from the key and those from the value. | FieldSelectionMapReduce.java