Column name from string

[#1]

Hi everyone,

I am working on a script that I would like to use a string as a column name, and use that column name in a formula, see below:

dt = Open( "$SAMPLE_DATA/Cities.jmp" );
//example column
dt << New Column("klaatu barada nikto", formula(3));
//suppose we don't know what exactly will be in 'a' as it is controlled by a for loop etc.
a = Concat Items( {"klaatu", "barada", "nikto"}, " " );

//can we get another column to take 'a' as an input?
dt << New Column("Gort", formula(column(a)*:Y));

When I use this however, it does not see "klaatu barada nikto" as a valid column, even though we created it before.

From other posts I have seen that the column() function can be used to assign a string to a column and I have used it in this way before, but in this instance it does not work. All we end up with is this:


Does anyone know a workaround for this? Thanks for any help in advance!

[#2 · Accepted solution]

Take a look at this Insert one expression into another using Eval Insert, Eval Expr, Parse, and Substitute 

dt = Open( "$SAMPLE_DATA/Cities.jmp" );
//example column
dt << New Column("klaatu barada nikto", formula(3));
//suppose we don't know what exactly will be in 'a' as it is controlled by a for loop etc.
a = Concat Items( {"klaatu", "barada", "nikto"}, " " );

//can we get another column to take 'a' as an input?

Eval(EvalExpr(dt << New Column("Gort", numeric, formula(ascolumn(expr(a))*:Y))));

[#3]

Fantastic! Thank you so much for your help.

[#4]

Jarmo, 

I'm using the same approach in one of my scripts and bumped into a problem: the formula in the new column will have that "a" column as this:

Formula(As Column("klaatu barada nikto")*:Y)

which means that if name of that column changes (and in my case it changes) this formula will become invalid. I need to somehow reference it not as As Column("name") but as :name - any way to do that?

[#5]

If I understand correctly what you want, you could try adding Name Expr

Names Default To Here(1);

dt = Open( "$SAMPLE_DATA/Cities.jmp" );
//example column
dt << New Column("klaatu barada nikto", formula(3));
//suppose we don't know what exactly will be in 'a' as it is controlled by a for loop etc.
a = Concat Items( {"klaatu", "barada", "nikto"}, " " );

Eval(EvalExpr(dt << New Column("Gort", numeric, formula(Expr(Name Expr(As Column(a)))*:Y))));