I have two variables, x and y.

x is an index variable that takes the average standardized response of some survey questions.
y contains the average percentile of the index by region.
I need to create a new variable, z that calculates the quantiles of the variable x based on the percentiles of y.

I have the R code to do this:

data <- within(data, z <- quantile(x, c(y), na.rm=T)) 

Is there an easy way to do this in STATA?

                                                    .