topic Re: How do I use a variable to reference a column in formula function? in Discussions

How do I use a variable to reference a column in formula function?

TraceTurtle5488 — Thu, 08 Jun 2023 16:38:56 GMT

Hi, I need to create a new column by apply formula on two existing column. I want to reference column through a variable rather than direct referencing. Here is the code , but formula seems doesn't recognize Column(ColVar). Anyone could help me to fix it? Thanks in advance.

yCol = Column("weight");
xCol = Column("height");
Bivariate( Y( yCol ), X( xCol) );
colVar ="$weight";
dt = currentdatatable();
dt<<new column("sum", formula(column(ColVar)+:height));

Re: How do I use a variable to reference a column in formula function?

txnelson — Thu, 02 Feb 2023 23:24:01 GMT

Because the formula entry is executed during the running of the column, not during the creation of the column, what is presented in the formula, needs to be the complete JSL required for processing.

Here is how I handle such issues

names default to here(1);
yCol =":weight";

dt = currentdatatable();
eval(parse("dt<<new column(\!"sum\!", formula(" || yCol || "+:height));"));

Re: How do I use a variable to reference a column in formula function?

Georg — Fri, 03 Feb 2023 11:59:58 GMT

Here is just another example using

eval(eval expr( expr ()))

but using the same strategy, implement the value of the variable into the formula.

Names Default To Here( 1 );

dt = Open( "$SAMPLE_DATA\Big Class.jmp" );

// get column names and show results
col_lst = dt << get column names();
my_cols= col_lst[4::5];
show(col_lst, my_cols);

// implement new formula
Eval( Eval Expr( dt << New Column( "sum of ", formula( sum(Expr(my_cols )) ) ) ) );