The cascading.operation.expression.ExpressionFunction function dynamically resolves a given expression using argument Tuple values as inputs to the fields specified in the expression.

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

String exp =
  "\"this \" + method + \" request was \" + size + \" bytes\"";
Fields fields = new Fields( "pretty" );
ExpressionFunction function =
  new ExpressionFunction( fields, exp, String.class );

assembly =
  new Each( assembly, new Fields( "method", "size" ), function );

// outgoing -> "pretty" = "this GET request was 1282652 bytes"

Above, we create a new String value form our expression. Note we must declare the type of every input Tuple value so the expression compiler knows how to treat the variables in the expression.

The cascading.operation.expression.ExpressionFilter filter dynamically resolves a given expression using argument Tuple values as inputs to the fields specified in the expression. Any Tuple that returns true for the given expression will be removed from the stream.

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

ExpressionFilter filter =
  new ExpressionFilter( "status != 200", Integer.TYPE );

assembly = new Each( assembly, new Fields( "status" ), filter );

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

Above, every line in the Apache log that does not have a "200" status will be filtered out. Notice that the "status" would be a String in this example if it was emitted from a RegexParser, if so the ExpressionFilter will coerce the value from a String to an int for the comparison.