error: "Expression does not fit available column types"

Question

Hi everyone,

In the following code I get the error: "Expression does not fit available column types" , and it happens during the formula evaluation..

I'm just trying to reference the same table as I am adding a new column to, such as subtracting two columns within the table called "dt" that I am adding a new column to... Can't figure out why it's not working.

dt = myTable();

cols = dt << GetColumnNames("String");

//Wait(3);

For(c=1, c<=NItems(cols), c++,

If( StartsWith(cols, "HTOL"),

dt << New Column(cols || " Δ", Numeric, Continuous, Formula( eval list( column(dt,4)) ) );

);

thanks

jeff

eveyja · Answer

Thanks PMroz! I ended up solving this one last night using verbage pretty similar to yours - I used something like this:

I think I used parse .. I don't remember if I had to use eval or not , I am about 60% sure I did.

If anyone needs me to , reply to this and I'll hunt up the exact syntax.

dt << new column( parse(cols || " Δ"), Numeric, Continuous, Formula(:^cols^ - :data 0))

pmroz · Answer

Similar technique as @stephen.pearson:

dt = New Table( "Demo", Add Rows( 3 ),

New Column( "data 0", Numeric, Continuous, Format( "Best", 12 ), Set Values( [1, 2, 3] ) ),

New Column( "data 100", Numeric, Continuous, Format( "Best", 12 ), Set Values( [4, 5, 6] ) ),

New Column( "data 200", Numeric, Continuous, Format( "Best", 12 ), Set Values( [7, 8, 9] ) )

);

cols = dt << get column names("String");

for (c = 1, c <= nitems(cols), c++,

if (starts with(uppercase(cols[c]), "DATA"),

new_col_expr = evalinsert("\[dt << new column( cols || " Î", Numeric, Continuous, Formula(:^cols^ - :data 0))]");

eval(parse(new_col_expr));

);

stephen_pearson · Answer

column(dt,c) is not the same as :data 100 as far as the formula is concerned.

One way to get this code to work is to use dynamic JSL, which evaluates the JSL before executing it.

// Not sure if this is quite the right syntx but you get the idea

TargetColumn = column(dt,c) <<Get Name("String");

//dynamic replacement to go inside the if clause

Eval(

Parse(

Eval Insert(

"\[

dt << New Column(cols || " delta", Numeric, Continuous, Formula( :^TargetColumn^ - :data 0 ) );

]"

)  )  );

If your column names have special characters in you may need to use :Name("^TargetColumn^") in the formula. This can still give odd results if there are ^/-+* symbols in the column name as the formula doesn't evaluate reliably.