Creation of the "Value Colors" property

[#1]

How can I script the creation of a set of value colors for a data table column without having to specify what they actually are?

I'm asking because I have an application that is expecting to find a "Value Colors" property associated with a selected column, and will crash if that property doesn't exist. I don't want to have to define the actual colors themselves because they're irrelevant: I just need there to be a Value Colors property.

I can do this very easily interactively by just right-clicking on the column in question, and selecting "Value Colors" from the list of properties, whereupon a default set is defined automatically for me. It's essentially this operation therefore that I need to script - and I'm guessing that the solution will be a single line of code, but I'm afraid I just can't see it. Can anyone help?

[#2]

You can use JSL like this:

column(dt, "Column 1") << Set Property( "Value Colors", {2 = 45, 3 = 46, 4 = 47} );

The way to figure this out is to

1. Create a small dummy table with a single numeric column

2. Manually add the Value Colors attribute

3. Click the little red triangle next to the table name and select Copy Table Script

4. Open up a JSL script window and paste the resulting code.  

It will look something like this:

New Table( "Untitled 14",
	Add Rows( 3 ),
	New Column( "Column 1",
		Numeric,
		"Continuous",
		Format( "Best", 12 ),
		Set Property( "Value Colors", {1 = -13977687, 2 = -3780931, 3 = -4222943} ),
		Set Selected,
		Set Values( [1, 2, 3] )
	)
);

[#3]

I was able to put a BS value colors property into a column doing this:

:Column 1 << Set Property("Value Colors",{});

Seems like the application really ought to be updated to work more robustly though.  Strange requirement.

[#4]

Many thanks both Peter and CWillden for your help; unfortunately I'm still not there - but I've been able to crystallize the problem a little.  The attached script shows where I've got to now: if I can resolve the final difficulty regarding how to create a list of expressions that I can then feed into the Value Colors property, I should be able to get what I need:

// Start of script;

clear log();

dt = Open( "$SAMPLE_DATA/Big Class.JMP" );

// The Value Colors property of the first column is initially empty;

show(:Name << get property("Value Colors"));

/*
	I now want to create a Value Colors property for this column,
	but I'd prefer to do it without having to identify all the names
	beforehand if possible.  Try CWillden's suggestion...
*/

:Name << set property("Value Colors", {});

// If I now try to color the cells by value, it DOES actually seem to have worked;

:Name << color cell by value(1);

// But the Value Colors property STILL only contains an empty list;

show(:Name << get property("Value Colors"));

/*
	Unfortunately I do actually need a populated list - and it looks like I can't do it
	without extracting the names explicity.  Here's one way I think I COULD do it...
*/

summarize(NamesList=by(:Name));
show(NamesList);

/*
	I now need to put those names into a list of expressions that follow the syntax
	shown in PMRoz's post, and use that list to define the Value Colors property I need.

	This next bit is WRONG - but you can see what I'm trying to do here.
	What I need inside ExprList is a list of names, each coupled with an integer from 3 onwards
	(to get some colors starting at red).  I suspect I should probably be using the Substitute
	and/or Eval Expr functions at this point, but I can't get the correct syntax.
*/

ExprList = {};
for(i=1, i<=nItems(NamesList), i++,
	insert into(ExprList, expr(NamesList[i] = (2+i)))
	);

show(ExprList);

// Then insert the resulting expression as the Value Colors property of the :Names column, and I should get what I want.

:Name << set property("Value Colors", ExprList);

// End of script.

[#5 · Accepted solution]

The ExprList is not being constructed properly.  You need to have the literal values in the list, not calculated values.  Here is one way to accomplish that

// Start of script;
Names Default To Here( 1 );
Clear Log();

dt = Open( "$SAMPLE_DATA/Big Class.JMP" );

Summarize( NamesList = by( :Name ) );
Show( NamesList );

// Build the ExprLIst to be exactly what the Value Colors
// list needs to be
ExprList = {};
For( i = 1, i <= N Items( NamesList ), i++,
	Eval(
		Substitute(
				Expr(
					Insert Into( ExprList, Expr( __Names__ = __color__ ) )
				),
			Expr( __Names__ ), NamesList[i],
			Expr( __color__ ), 2 + i
		)
	)
);

Show( ExprList );

// Then insert the resulting expression as the Value Colors property of the :Names column, and I should get what I want.
:Name << set property( "Value Colors", ExprList );

// The Value Colors property is correct;
Show( :Name << get property( "Value Colors" ) );

[#6]

Perfect!  Always better to ask the experts than try to get that sort of construction right :)

Many thanks, Jim!