How do I calculate a new column with row-dependent operations determined by a grouping label?

[#1]

I created a stacked table that has a column X corresponding to x-coordinates, a column Label with a grouping label, and finally the Data column. Suppose the set of x-coordinates shared for all collected data are [1,2,3,4,5,6,7,8,9,10], there are three groups A,B,C, and the data are arbitrary numbers. I want to make a new column where the value from Data is normalized within each group (A, B, C) by the value from that group at a specific coordinate, let's say X=3. In other words, for every row where Label = A, divide Data by the value of Data where X=3 AND Label=A. Repeat for B and C. I can think of approaches with if and for loops, but I suspect that is a pretty inefficient way to do the calculation at scale.

[#2 · Accepted solution]

use the Normalization GUI 

[#3]

If you prefer a script: 
use the GUI once to create a normalized column, then steal the code.

[#4]

Wow that's exactly what I needed, thank you!