The cascading.tuple.Fields.ALL constant is a wildcard that represents all the current available fields.

// incoming -> first, last, age

String expression = "first + \" \" + last";
Fields fields = new Fields( "full" );
ExpressionFunction full =
  new ExpressionFunction( fields, expression, String.class );

assembly =
  new Each( assembly, new Fields( "first", "last" ), full, Fields.ALL );

// outgoing -> first, last, age, full

The cascading.tuple.Fields.RESULTS constant is used to represent the field names of the current operations return values. This Fields set may only be used as an output selector on a pipe, causing the pipe to output a tuple containing the operation results.

// incoming -> first, last, age

String expression = "first + \" \" + last";
Fields fields = new Fields( "full" );
ExpressionFunction full =
  new ExpressionFunction( fields, expression, String.class );

Fields firstLast = new Fields( "first", "last" );
assembly =
  new Each( assembly, firstLast, full, Fields.RESULTS );

// outgoing -> full

The cascading.tuple.Fields.REPLACE constant is used as an output selector to inline-replace values in the incoming tuple with the results of an operation. This convenient Fields set allows operations to overwrite the value stored in the specified field. The current operation must either specify the identical argument selector field names used by the pipe, or use the ARGS Fields set.

// incoming -> first, last, age

// coerce to int
Identity function = new Identity( Fields.ARGS, Integer.class );

Fields age = new Fields( "age" );
assembly = new Each( assembly, age, function, Fields.REPLACE );

// outgoing -> first, last, age

The cascading.tuple.Fields.SWAP constant is used as an output selector to swap the operation arguments with its results. Neither the argument and result field names, nor the size, need to be the same. This is useful for when the operation arguments are no longer necessary and the result Fields and values should be appended to the remainder of the input field names and Tuple.

// incoming -> first, last, age

String expression = "first + \" \" + last";
Fields fields = new Fields( "full" );
ExpressionFunction full =
  new ExpressionFunction( fields, expression, String.class );

Fields firstLast = new Fields( "first", "last" );
assembly = new Each( assembly, firstLast, full, Fields.SWAP );

// outgoing -> age, full

The cascading.tuple.Fields.ARGS constant is used to let a given operation inherit the field names of its argument Tuple. This Fields set is a convenience and is typically used when the Pipe output selector is RESULTS or REPLACE. It is specifically used by the Identity Function when coercing values from Strings to primitive types.

// incoming -> first, last, age

// coerce to int
Identity function = new Identity( Fields.ARGS, Integer.class );

Fields age = new Fields( "age" );
assembly = new Each( assembly, age, function, Fields.REPLACE );

// outgoing -> first, last, age

The cascading.tuple.Fields.GROUP constant represents all the fields used as grouping key in the most recent grouping. If no previous grouping exists in the pipe assembly, GROUP represents all the current field names.

// incoming -> first, last, age

assembly = new GroupBy( assembly, new Fields( "first", "last" ) );

FieldJoiner full = new FieldJoiner( new Fields( "full" ), " " );

assembly = new Each( assembly, Fields.GROUP, full, Fields.ALL );

// outgoing -> first, last, age, full

The cascading.tuple.Fields.VALUES constant represents all the fields not used as grouping fields in a previous Group. That is, if you have fields "a", "b", and "c", and group on "a", Fields.VALUES will resolve to "b" and "c".

// incoming -> first, last, age

assembly = new GroupBy( assembly, new Fields( "age" ) );

FieldJoiner full = new FieldJoiner( new Fields( "full" ), " " );

assembly = new Each( assembly, Fields.VALUES, full, Fields.ALL );

// outgoing -> first, last, age, full

The cascading.tuple.Fields.UNKNOWN constant is used when Fields must be declared, but it's not known how many fields or what their names are. This allows for processing tuples of arbitrary length from an input source or some operation. Use this Fields set with caution.

// incoming -> line

RegexSplitter function = new RegexSplitter( Fields.UNKNOWN, "\t" );

Fields fields = new Fields( "line" );
assembly =
  new Each( assembly, fields, function, Fields.RESULTS );

// outgoing -> unknown

The cascading.tuple.Fields.NONE constant is used to specify no fields. Typically used as an argument selector for Operations that do not process any Tuples, like cascading.operation.Insert.

// incoming -> first, last, age

Insert constant = new Insert( new Fields( "zip" ), "77373" );

assembly = new Each( assembly, Fields.NONE, constant, Fields.ALL );

// outgoing -> first, last, age, zip