I agree that these messages are powerful and make scripting much easier than it would be without them.
Their syntax and usage is straightforward. These messages take Boolean arguments. Any expression that evaluates to true or false is valid. Also, any numerical result will work, where 0 is interpreted as false and any other value is interpreted as true. The expression is evaluated row-wise, substituting the column reference in the expression with the value for that column in the current row.
Using Big Class as an example, you select all female observations with Current Data Table() << Select Where( :sex == "F" ). In this case, the column reference is literal. If you are using a column reference stored in a variable instead, then you must append "[]" after the column name. So my example would become col = Column( "sex" ); Current Data Table() << Select Where( :col[] == "F" ).
Of course the Boolean expression could select on multiple criteria by using other logical functions, as in Current Data Table() << Select Where( :sex == "F" & :age == 12 ).
That is really about all there is to it.
