Formula for normalizing data to control mean

[#1]

Here's the very simple situation I have:

Column A: Continuous data on treatment levels in an experiment.  0 = controls

Column B: Continuous data that is the response metric to the treatment. 

Column C: Formula that calculates response metric from Column B normalized (i.e. divided by) the mean of the responses in the controls (rows where Column A=0).

How do I write the formula in Column C to do this normalization of Column B to the control mean?

I think it will involve creating a local variable that uses the Col Mean function conditional to the Rows in Column A that are = 0. 

I don't know how to make that conditional work for the multiple rows that need to be selected for calculation of the mean of the controls.

I know that the Col Mean function calculates the mean of all the data in Column B, and that using a By variable can calculate means for each value of Column A. But, I want to calculate a single mean for the values of Column B where Column A are = 0 and use that single mean as an argument in Column C for calculating an equation (Column C=Column B/Mean of Column B where Column A=0) in every row of the table.

I'm using JMP 16.

[#2]

One option is to use If statement inside the Col Mean

Col Mean(If(:Column 1 == 0, :Column 2, .))

If Column A has first row as 0 you can also use As Constant() to calculate the mean

As Constant(Col Mean(:Column 2, :Column 1))

I have attached example table with both mean calculations. You can of course just take the mean calculation and use that then in single column which will calculate your final data.

[#3 · Accepted solution]

Thanks jthi, I took your example and wrote the formula equation for Column 3 so the normalization, it all happens in that column as follows,

:Column 2 / Col Mean( If( :Column 1 == 0, :Column 2, . ) )

I didn't need to create a local variable.  The Col Mean function apparently does that in the background.

I appreciate your insight!  Thanks!

Vince