How to add columns with empty data

[#1]

I have a table similar to this:

	x	y	z		xyz	xyz
aa	1	2			.	3
bb					.	.
cc	2		3		.	5

The columns have rows containing both numeric and empty data.

I want to create a new column (xyz) where I add the data in column x, y and z.

In other words, I want the result to look like the green xyz-column.

The problem is, when I run my script, I get the result in the red xyz-column..

How do I add columns with empty data?

I use the following script to create the xyz-column:

dt << New Column("xyz",

         Numeric,

         Formula(:Name("x")+:Name("y")+:Name("z")

         )

         );

[#2 · Accepted solution]

Use:

dt << New Column( "xyz", Numeric, Formula( Sum( :x, :y,:z ) ) );

 The Sum() function ignores missing values.

[#3]

Thank you, it works :)