diff --git a/doc/downsample.md b/doc/downsample.md
new file mode 100644
index 0000000..0b80ed7
--- /dev/null
+++ b/doc/downsample.md
@@ -0,0 +1,5 @@
+# Downsampling the Training Data
+
+```clojure
+:downsample-rate
+```
\ No newline at end of file
diff --git a/src/propeller/downsample.cljc b/src/propeller/downsample.cljc
new file mode 100644
index 0000000..8c85ab8
--- /dev/null
+++ b/src/propeller/downsample.cljc
@@ -0,0 +1,18 @@
+(ns propeller.downsample)
+
+(defn assign-indices-to-data
+  "assigns an index to each training case in order to differentiate them when downsampling"
+  [{:keys [training-data]}]
+  (map (fn [data-map index]
+         (let [data-m (if (map? data-map) data-map (assoc {} :data data-map))] ;if data is not in a map, make it one
+           (assoc data-m :index index)))
+       training-data (range (count training-data))))
+
+(defn select-downsample-random
+  "Selects a downsample from the training cases and returns it"
+  [{:keys [downsample-rate training-data]}]
+  (take (int (* downsample-rate (count training-data))) (shuffle training-data)))
+
+(defn update-case-data
+  "updates the case metadata field of argmap, should be called after evaluation of individuals"
+  [argmap])
\ No newline at end of file
diff --git a/test/propeller/utils_test.cljc b/test/propeller/utils_test.cljc
index e450a38..1212e24 100644
--- a/test/propeller/utils_test.cljc
+++ b/test/propeller/utils_test.cljc
@@ -1,7 +1,8 @@
 (ns propeller.utils-test
   (:require [clojure.test :as t]
             [propeller.utils :as u]
-            [propeller.simplification :as s]))
+            [propeller.simplification :as s]
+            [propeller.downsample :as ds]))
 
 (t/deftest first-non-nil-test
   (t/is (= 1 (u/first-non-nil '(1 2 3))))
@@ -22,57 +23,89 @@
 
 (t/deftest random-instruction-test
   (t/is
-    (letfn [(instruct [] 1)]
-      (let [test (u/random-instruction [instruct 2])]
-            (if (= 1 test)
-              true
-              (= 2 test))))))
+   (letfn [(instruct [] 1)]
+     (let [test (u/random-instruction [instruct 2])]
+       (if (= 1 test)
+         true
+         (= 2 test))))))
 
 (t/deftest count-points-test
   (t/is (= 6 (u/count-points '(:a :b (:c :d)))))
   (t/is (= 1 (u/count-points '())))
   (t/is (= 2 (u/count-points '(:a)))))
 
-(t/testing "choose-random-k"
-  (t/testing "should return indices that are a member of the original array"
-    (t/is (every? identity (map #(contains? (set (range 10)) %) (s/choose-random-k 3 (range 10))))))
-  (t/testing "should return a list of size k"
-    (t/is (= (count (s/choose-random-k 7 (range 10))) 7))))
+(t/deftest choose-random-k-test
+  (t/testing "choose-random-k"
+    (t/testing "should return indices that are a member of the original array"
+      (t/is (every? identity (map #(contains? (set (range 10)) %) (s/choose-random-k 3 (range 10))))))
+    (t/testing "should return a list of size k"
+      (t/is (= (count (s/choose-random-k 7 (range 10))) 7)))))
 
-(t/testing "delete-at-indices"
-  (t/testing "should actually remove indicated items"
-    (t/is (= '(:hi1 :hi2) (s/delete-at-indices '(0 3) '(:hi0 :hi1 :hi2 :hi3)))))
-  (t/testing "should work with numerical indices"
-    (t/is (= '(:hi1 :hi2 :hi3) (s/delete-at-indices '(0) '(:hi0 :hi1 :hi2 :hi3)))))
-  (t/testing "should not delete anything for index out of bounds"
-    (t/is (= '(:hi1 :hi2 :hi3) (s/delete-at-indices '(0 10) '(:hi0 :hi1 :hi2 :hi3))))
-    (t/is (= '(:hi1 :hi2 :hi3) (s/delete-at-indices '(0 -10) '(:hi0 :hi1 :hi2 :hi3))))
-    (t/is (= '(:hi1 :hi2 :hi3) (s/delete-at-indices '(-0 -10) '(:hi0 :hi1 :hi2 :hi3)))))
-  (t/testing "should only delete at single index once"
-    (t/is (= '(:hi1 :hi2) (s/delete-at-indices '(0 0 0 0 3 3 3) '(:hi0 :hi1 :hi2 :hi3)))))
-  (t/testing "should return empty list when deleting from empty list"
-    (t/is (= '() (s/delete-at-indices '(0) '()))))
-  (t/testing "should be able to delete at arbitrary indices"
-    (t/is (= (count (s/delete-at-indices (s/choose-random-k 3 (range 10)) (range 10))) 7))))
 
-(t/testing "delete-random-k"
-  (t/testing "should remove the correct amount of items"
-    (t/is (= (count (s/delete-k-random 3 (range 10))) 7))
-    (t/is (= (count (s/delete-k-random 10 (range 10))) 0))
-    (t/is (= (count (s/delete-k-random 0 (range 10))) 10)))
-  (t/testing "should not fail if k >> size of collection"
-    (t/is (= (count (s/delete-k-random 300 (range 10))) 0))
-    (t/is (= (s/delete-k-random 300 '(:hi1 :hi2 :hi3)) '())))
-  (t/testing "should not fail if the collection is empty"
-    (t/is (= (count (s/delete-k-random 300 '())) 0))
-    (t/is (= (count (s/delete-k-random 0 '())) 0)))
-  (t/testing "should maintain order of the remaining items"
-    (t/is (apply < (s/delete-k-random 3 (range 10))))))
+(t/deftest delete-at-indices-test
+  (t/testing "delete-at-indices"
+    (t/testing "should actually remove indicated items"
+      (t/is (= '(:hi1 :hi2) (s/delete-at-indices '(0 3) '(:hi0 :hi1 :hi2 :hi3)))))
+    (t/testing "should work with numerical indices"
+      (t/is (= '(:hi1 :hi2 :hi3) (s/delete-at-indices '(0) '(:hi0 :hi1 :hi2 :hi3)))))
+    (t/testing "should not delete anything for index out of bounds"
+      (t/is (= '(:hi1 :hi2 :hi3) (s/delete-at-indices '(0 10) '(:hi0 :hi1 :hi2 :hi3))))
+      (t/is (= '(:hi1 :hi2 :hi3) (s/delete-at-indices '(0 -10) '(:hi0 :hi1 :hi2 :hi3))))
+      (t/is (= '(:hi1 :hi2 :hi3) (s/delete-at-indices '(-0 -10) '(:hi0 :hi1 :hi2 :hi3)))))
+    (t/testing "should only delete at single index once"
+      (t/is (= '(:hi1 :hi2) (s/delete-at-indices '(0 0 0 0 3 3 3) '(:hi0 :hi1 :hi2 :hi3)))))
+    (t/testing "should return empty list when deleting from empty list"
+      (t/is (= '() (s/delete-at-indices '(0) '()))))
+    (t/testing "should be able to delete at arbitrary indices"
+      (t/is (= (count (s/delete-at-indices (s/choose-random-k 3 (range 10)) (range 10))) 7)))))
 
-(t/testing "auto-simplify-plushy"
-  (t/testing "should handle having an empty plushy"
-    (t/is (= (s/auto-simplify-plushy {} '() 100 (fn [argmap data plushy] 0) {} 3 false) '())))
-  (let [plushy '(:exec_dup 1 :integer_add close :in1 :integer_add 0 :in1 :in1 :integer_mult :integer_add)]
-        (t/testing "should decrease size of plushy that always has perfect scores"
-              (t/is (< (count (s/auto-simplify-plushy {} plushy 5 (fn [argmap data plushy] 0) {} 3 false)) (count plushy)))
-              (t/is (< (count (s/auto-simplify-plushy {} plushy 1 (fn [argmap data plushy] 0) {} 10 false)) (count plushy))))))
\ No newline at end of file
+(t/deftest delete-random-k-test
+  (t/testing "delete-random-k"
+    (t/testing "should remove the correct amount of items"
+      (t/is (= (count (s/delete-k-random 3 (range 10))) 7))
+      (t/is (= (count (s/delete-k-random 10 (range 10))) 0))
+      (t/is (= (count (s/delete-k-random 0 (range 10))) 10)))
+    (t/testing "should not fail if k >> size of collection"
+      (t/is (= (count (s/delete-k-random 300 (range 10))) 0))
+      (t/is (= (s/delete-k-random 300 '(:hi1 :hi2 :hi3)) '())))
+    (t/testing "should not fail if the collection is empty"
+      (t/is (= (count (s/delete-k-random 300 '())) 0))
+      (t/is (= (count (s/delete-k-random 0 '())) 0)))
+    (t/testing "should maintain order of the remaining items"
+      (t/is (apply < (s/delete-k-random 3 (range 10)))))))
+
+(t/deftest auto-simplify-plushy-test
+  (t/testing "auto-simplify-plushy"
+    (t/testing "should handle having an empty plushy"
+      (t/is (= (s/auto-simplify-plushy {} '() 100 (fn [argmap data plushy] 0) {} 3 false) '())))
+    (let [plushy '(:exec_dup 1 :integer_add close :in1 :integer_add 0 :in1 :in1 :integer_mult :integer_add)]
+      (t/testing "should decrease size of plushy that always has perfect scores"
+        (t/is (< (count (s/auto-simplify-plushy {} plushy 5 (fn [argmap data plushy] 0) {} 3 false)) (count plushy)))
+        (t/is (< (count (s/auto-simplify-plushy {} plushy 1 (fn [argmap data plushy] 0) {} 10 false)) (count plushy)))))))
+
+(t/deftest assign-indices-to-data-test
+  (t/testing "assign-indices-to-data"
+    (t/testing "should return a map of the same length"
+      (t/is (= (count (ds/assign-indices-to-data {:training-data (range 10)})) 10))
+      (t/is (= (count (ds/assign-indices-to-data {:training-data (range 0)})) 0)))
+    (t/testing "should return a map where each element has an index key"
+      (t/is (every? #(:index %) (ds/assign-indices-to-data {:training-data (map #(assoc {} :input %) (range 10))}))))
+    (t/testing "should return distinct indices"
+      (t/is (= (map #(:index %) (ds/assign-indices-to-data {:training-data (range 10)})) (range 10))))))
+
+(t/deftest select-downsample-random-test
+  (t/testing "select-downsample-random"
+    (t/testing "should select the correct amount of elements"
+      (t/is (= (count (ds/select-downsample-random {:training-data (range 10) :downsample-rate 0.1})) 1))
+      (t/is (= (count (ds/select-downsample-random {:training-data (range 10) :downsample-rate 0.2})) 2))
+      (t/is (= (count (ds/select-downsample-random {:training-data (range 10) :downsample-rate 0.5})) 5)))
+    (t/testing "should not return duplicate items (when called with set of numbers)"
+      (t/is (= (count (set (ds/select-downsample-random {:training-data (range 10) :downsample-rate 0.1}))) 1))
+      (t/is (= (count (set (ds/select-downsample-random {:training-data (range 10) :downsample-rate 0.2}))) 2))
+      (t/is (= (count (set (ds/select-downsample-random {:training-data (range 10) :downsample-rate 0.5}))) 5)))
+    (t/testing "should round down the number of elements selected if not whole"
+      (t/is (= (count (ds/select-downsample-random {:training-data (range 3) :downsample-rate 0.5})) 1))
+      (t/is (= (count (ds/select-downsample-random {:training-data (range 1) :downsample-rate 0.5})) 0)))
+    (t/testing "should not return more elements than available"
+      (t/is (= (count (ds/select-downsample-random {:training-data (range 10) :downsample-rate 2})) 10))
+      (t/is (= (count (ds/select-downsample-random {:training-data (range 10) :downsample-rate 1.5})) 10)))))