topic Re: Expression Not Evaluating. in Discussions

Expression Not Evaluating.

SpannerHead — Fri, 17 Apr 2026 17:35:44 GMT

Always mystified by how to use Eval Expr correctly. I have this pop up that asks for a wildcard column name selection and assigns it as "Divider"

nw = New Window( "Does the Data Contain Experimental Cells?",
	<<Modal,
	V List Box(
		Align( "right" ),
		H List Box(
			Panel Box( "Dividing Column", clb = Filter Col Selector( dt, all ) ),
			Panel Box( "Select Cell Identification Column",
				Lineup Box( N Col( 2 ), Spacing( 5 ),
					Button Box( "Divider", clbY << Append( clb << Get Selected ) ),
					clbY = Col List Box( MinItems( 1 ), MaxItems( 1 ), nlines( 1 ) ),
					Button Box( "Remove",
						clbY << Remove Selected;
						clbEffects << Remove Selected;
					)
				)
			)
		),
		H List Box(
			Button Box( "OK", yVars = clby << Get Items( "Column Reference" ) ),
			Button Box( "Cancel" )
		)
	)
);
Try( Divider = yVars[1] );

I then try to evaluate the object in a column formula and whatever combination of Eval(Eval Expr( I use, nothing seems to work.

If( N Items( yVars ) == 0,
	Data Table( "HIRP" ) << New Column( "Average Active Power",
		Numeric,
		"Continuous",
		Format( "Best", 12 ),
		Formula(
			If(
				:Heater == "Reader", Col Mean( :HL_R_HEAT, :Heater ),
				Contains( :Heater, "Writer" ),
					Col Mean( :HL_W_HEAT, :Heater )
			)
		)
	),
	Eval(Eval Expr(Data Table( "HIRP" ) << New Column( "Average Active Power",
		Numeric,
		"Continuous",
		Format( "Best", 12 ),
		Formula(
			If(
				:Heater == "Reader", Col Mean( :HL_R_HEAT, :Heater, As Column(Expr(Divider)) ),
				Contains( :Heater, "Writer" ),
					Col Mean( :HL_W_HEAT, :Heater, :HD_NUM, As Column(Expr(Divider)) )
			)
		)
	)
)));

Re: Expression Not Evaluating.

jthi — Fri, 17 Apr 2026 17:43:08 GMT

Change

As Column(Expr(Divider))

Expr(NameExpr(As Column(dt, Divider)))

Name Expr() isn't necessary but you will end up with "nicer looking" formulas when you use that.

Names Default To Here(1); 

dt = open("$SAMPLE_DATA/Big Class.jmp");

div = "weight";
Eval(EvalExpr(
	dt << New Column("C", Numeric, Continuous, Formula(
		:Height / Expr(NameExpr(AsColumn(dt, div)))
	))
));

Also, you can test your expression evaluations by just running the EvalExpr part instead of the whole Eval(EvalExpr(...

Re: Expression Not Evaluating.

SpannerHead — Fri, 17 Apr 2026 18:04:27 GMT

Needed a small tweak but worked, Thanks

If( N Items( yVars ) == 0,
	Data Table( "HIRP" ) << New Column( "Average Active Power",
		Numeric,
		"Continuous",
		Format( "Best", 12 ),
		Formula(
			If(
				:Heater == "Reader", Col Mean( :HL_R_HEAT, :Heater ),
				Contains( :Heater, "Writer" ),
					Col Mean( :HL_W_HEAT, :Heater )
			)
		)
	),
	Eval(Eval Expr(Data Table( "HIRP" ) << New Column( "Average Active Power",
		Numeric,
		"Continuous",
		Format( "Best", 12 ),
		Formula(
			If(
				:Heater == "Reader", Col Mean( :HL_R_HEAT, :Heater, Expr(NameExpr(As Column( Divider))) ),
				Contains( :Heater, "Writer" ),
					Col Mean( :HL_W_HEAT, :Heater, :HD_NUM, Expr(NameExpr(As Column( Divider))) )
			)
		)
	)
)));

Re: Expression Not Evaluating.

SpannerHead — Fri, 17 Apr 2026 19:40:21 GMT

Jarmo

I have something that works now but I don't understand why it works. Is there somewhere that gives a clear description of how the evaluation methodology should be employed? Hoping to spend less time on here searching for answers.

Re: Expression Not Evaluating.

jthi — Fri, 17 Apr 2026 19:51:43 GMT

Scripting Guide > Programming Methods > Advanced Expressions, Macros, and Lists

Morgan, J. (2010). “Expression Handling Functions: Part I.” JMPer Cable 26:15–19.