How to use Column index (instead of Column name) in a formula.Hi,
I am trying to do this in a for loop:
In current table, I have 14 Columns. Column #3~#14 were named as "Step 1" to "Step 12".
In the for loop, I want to create Column #15 (named as "Delta Step i" for i = 2, i <=12, i++), which is calculated with formula (Col(4) -Col(2)). Then Column#3 was deleted. The same formula will be reused in the next iteration.
Two problems here,
1) my formula doesn't work as there is no value in Column#15 of the output table;
2)I am worried that once column3 is detected, the values in Column15 (actually Column 14, after Column 3 is deleted) will be gone.
Here is my script.
For(i=2,i<=15,i++,
DeltaStep = "Delta Step "||Char(i);
New Column(DeltaStep)<<FORMULA></FORMULA>
I also tried this, but not working, either.
For(i=2,i<=12,i++,
DeltaStep = "Delta Step "||Char(i);
Pre = Column(3) << getname;
Pst = Column(4) << getname;
New Column(DeltaStep)<<FORMULA></FORMULA>
Re: How to use Column index (instead of Column name) in a formula.Good catch! People often forget that Column(#) or Column("name") need the empty brackets ( [] ) or the As Column() wrapper for row-wise calculations. I like to think of the reference as a pointer to the column header and attributes and the ref[] exposes the vector or list of values.
Regarding delete columns, it is a table message. You could have alo used the JSL below without selecting the column beforehand.
dt << Delete Columns( 3 );
Another common mistake is trying to delete a column that is used as an argument for another column formula. Suppose Col 4 uses a formula that references Col 3. You must remove the dependent formula in Col 4, then you can delete Col 3.
This is another reason for using << Set Each Value(expression) vs. Formula (expression) for most cases, then the new columns are not locked, and dependencies do not exist.
Re: How to use Column index (instead of Column name) in a formula.I am also wrong for the "delete columns" expr.
Attached the correct script here, please let me know if any better way to do this.
Thanks!
For(i=2,i<=12,i++,
DeltaStep = "Delta Step "||Char(i);
New Column(DeltaStep,formula(Column(4)[] - Column(3)[]));
Column(3) << Set Selected;
dt << Delete Columns
);
Re: How to use Column index (instead of Column name) in a formula.I think I found why I am not doing this correctly...
For the first script in my post, I should add [] after Column(3)...
Thanks,
Zihao
