Evaluating Dif Function by Column

[#1]

I'm trying to evaluate the difference between two rows using the "Dif" function; however, the evaluation is continuous and has no regard for other columns. For example, with the "Big Class" DT I run the script below, but it will still compute the weight difference between a male and female. Is there any way around this?

dt = Current Data Table();

dt << Sort( By( :age, :sex ), Order( Ascending, Ascending ) );

dt << New Column("Weight Delta", Formula(Dif(:weight)));

[#2]

I believe this formula will do what you want.

If( :sex == Lag( :sex ),
	Dif( :weight ),
	.
)