Here Identity passes its arguments out as results, thanks to the Fields.ARGS field declaration.

// incoming -> "ip", "time", "method", "event", "status", "size"

Identity identity = new Identity( Fields.ARGS );
pipe = new Each( pipe, new Fields( "ip", "method" ), identity,
                 Fields.RESULTS );

// outgoing -> "ip", "method"

In practice the field declaration can be left out as Field.ARGS is the default declaration for the Identity function. Additionally Fields.RESULTs can be left off as it is the default for the Every pipe.

// incoming -> "ip", "time", "method", "event", "status", "size"

pipe = new Each( pipe, new Fields( "ip", "method" ), new Identity() );

// outgoing -> "ip", "method"

Here Identity renames the incoming arguments. Since Fields.RESULTS is implied, the incoming Tuple is replaced by the arguments selected and given new field names as declared on Identity.

// incoming -> "ip", "method"

Identity identity = new Identity( new Fields( "address", "request" ) );
pipe = new Each( pipe, new Fields( "ip", "method" ), identity );

// outgoing -> "address", "request"

In the above example, if there were more fields than "ip" and "method", it would work fine, all the extra fields would be discarded. If the same was true for the next example, the planner would fail.

// incoming -> "ip", "method"

Identity identity = new Identity( new Fields( "address", "request" ) );
pipe = new Each( pipe, Fields.ALL, identity );

// outgoing -> "address", "request"

Since Fields.ALL is the default argument selector for the Each pipe, it can be left out.

// incoming -> "ip", "method"

Identity identity = new Identity( new Fields( "address", "request" ) );
pipe = new Each( pipe, identity );

// outgoing -> "address", "request"

Here we rename a single field, but return it along with an input Tuple field as the result.

// incoming -> "ip", "time", "method", "event", "status", "size"

Fields fieldSelector = new Fields( "address", "method" );
Identity identity = new Identity( new Fields( "address" ) );
pipe = new Each( pipe, new Fields( "ip" ), identity, fieldSelector );

// outgoing -> "address", "method"

Here we replace the Tuple String values "status" and "size" with int and long, respectively.

// incoming -> "ip", "time", "method", "event", "status", "size"

Identity identity = new Identity( Integer.TYPE, Long.TYPE );
pipe = new Each( pipe, new Fields( "status", "size" ), identity );

// outgoing -> "status", "size"

Or we can replace just the Tuple String value "status" with int while keeping all the other values in the output Tuple.

// incoming -> "ip", "time", "method", "event", "status", "size"

Identity identity = new Identity( Integer.TYPE );
pipe = new Each( pipe, new Fields( "status" ), identity,
                 Fields.REPLACE );

// outgoing -> "ip", "time", "method", "event", "status", "size"