Divide column by reference point with conditions

[#1]

Hi. I have a problem I can't get my head around. 

I am trying to create a new column which consists of another column divided by a reference point, but the problem is I have some conditions to include.

For simplicity I have added a generated datafile which I will refer to.

What I want to do is to take column Z and divide it by Z|X=c within each Y-group. The Y-groups are as you can tell not the same size.

SO C is the reference point, and for all Y-groups (1-9) I want to take column Z, and divide it by Z|X=c.

That is, in the new column all values where X=c will be 1 and the others will be Z / (Z|X=c).

I apologize for not being able to formulate myself in clearer terms, for various reasons I can not show my real dataset and English is not my native tounge. 

Any help is greatly appreciated.

V

[#2 · Accepted solution]

Here is one formula that works

currentY = :Y;
:Z / :Z[(Current Data Table() << get rows where( :X == "c" & :Y == currentY ))[1]];

[#3]

Haha this was way easier than I thought it would be.

Thank you very much.