For a side-project I went back into Lispstat, which was developed in the 90s, to perform basic biostatistical analysis. At that time, there was no such thing like a data frame, but only data arrays composed of numerical values thta could be imported from a space delimited text file. Usually, you “selected” the variables you were interested in one at a time. Assuming you have two series of values (i.e., two variables), you can split a response variable by a grouping factor like this:

(def geno1 (select age (which (= 1 genotype))))
(def geno2 (select age (which (= 2 genotype))))
(def geno3 (select age (which (= 3 genotype))))

I often use a loop to generate variable name with a common prefix or suffix. In R it is easily done using a for loop and assign (see this example), while in Stata it can be done in a forvalues or foreach construct. Here is an example from my Stata Starter Kit (draft):

xtile weightc = weight, nq(4)
quietly tabulate weightc, gen(weightc)
drop weightc
local i = 0
foreach v of varlist weightc1-weightc4 {
  local i = `i' + 1
  rename `v' w`i'
}
list w* in 1/5

Lispstat was built on the XLISP dialect of Lisp, which means it is mostly the same as Common Lisp except that something are missing here and there, most notably the loop macro. There are several constructs available for iterating over a range or a list, like do, dotimes and dolist. Since we cannot use dotimes to iterate over a sequence starting at a value other than zero,¹ let’s try with dolist:

(dolist (n (iseq 1 3))
    (set (intern (concatenate 'string "GENO"
                              (write-to-string n)))
         (select age (which (= n genotype)))))

Dont' forget that variables are represented internally as uppercase symbol, so even if you call your variable geno1 at the prompt or in an expression, it really is GENO1 in the environment.

It is a little more verbose than the previous expressions, but once converted to a macro, it can be reused many times.