How to refer to a column in Group By() message in Bivariate Platform

[#1]

I have a Bivariate Platform scripted like this:

Fit Group(
	biv = Bivariate( Y(Eval(Y_parameters)), X(Eval(X_parameters)), Group By (groupByColumn[1]),
			SendToReport(...)
	)
)

where 

Y_Parameters = {"Param1", "Param2"};
X_Parameters = {"Radius"};
groupByColumn = {"Lot ID"};

So, it works ONLY if my groupByColumn is a list of strings, and only if I refer to it as groupByColumn[1]

if I say 

stringGroupByColumn = groupByColumn[1]

and then use 

Group By (stringGroupByColumn)

it won't work.

WHY?

If I say 

groupByColumn = "Lot ID";

and then use it - it also won't work. WHY?

[#2]

The reason it does not work is because you are not setting a variable value, but rather you are passing a message to thr Bivariate Platform.  The proper syntax is

Biv << Group By( :lot ID );

See the Scripting Index for examples

[#3]

Ok, what if I don't know the column name and I just picked it from Col List Box?

When I get columns from Col List Box using << Get Items it returns them as:

Y_Parameters = {"Param1", "Param2"};

in case of the Col List Box that I use to cast Group By it only returns one due to the settings of Col List Box, it returns it as this:

groupByColumn = {"SomeRandomColumn"};

the only way to use it is 

Group By (groupByColumn[1])

[#4]

Ok, looks like it works this way:

 Y_parameters = colListYParameter << Get Items;
X_parameters = colListXParameter << Get Items;
groupByColumnNames = colListBox << Get Items;
groupByColumn = Column(groupByColumnNames [1]);

biv = Bivariate( Y(Eval(Y_parameters)), X(Eval(X_parameters)),Group By (groupByColumn), Fit Spline( 0.1, Standardized), 
			SendToReport(...)
)

Basically, I wanted to use "clean" variable, that is just a reference to column, without it being a subscript of a string array.