Merge pull request #1283 from primo-ppcg/mean-partition

Update `partition`, `mean`

src/boot/boot.janet

@@ -643,7 +643,12 @@
 (defn mean
   "Returns the mean of xs. If empty, returns NaN."
   [xs]
-  (/ (sum xs) (length xs)))
+  (if (lengthable? xs)
+    (/ (sum xs) (length xs))
+    (do
+      (var [accum total] [0 0])
+      (each x xs (+= accum x) (++ total))
+      (/ accum total))))
 
 (defn product
   "Returns the product of xs. If xs is empty, returns 1."
@@ -1730,20 +1735,28 @@
         ret))
     @[]))
 
+(defn- partition-slice
+  [f n ind]
+  (var [start end] [0 n])
+  (def len (length ind))
+  (def parts (div len n))
+  (def ret (array/new-filled parts))
+  (forv k 0 parts
+    (put ret k (f ind start end))
+    (set start end)
+    (+= end n))
+  (if (< start len)
+    (array/push ret (f ind start)))
+  ret)
+
 (defn partition
   ``Partition an indexed data structure `ind` into tuples
   of size `n`. Returns a new array.``
   [n ind]
-  (var i 0) (var nextn n)
-  (def len (length ind))
-  (def ret (array/new (math/ceil (/ len n))))
-  (def slicer (if (bytes? ind) string/slice tuple/slice))
-  (while (<= nextn len)
-    (array/push ret (slicer ind i nextn))
-    (set i nextn)
-    (+= nextn n))
-  (if (not= i len) (array/push ret (slicer ind i)))
-  ret)
+  (cond
+    (indexed? ind) (partition-slice tuple/slice n ind)
+    (bytes? ind) (partition-slice string/slice n ind)
+    (partition-slice tuple/slice n (values ind))))
 
 ###
 ###

test/suite-boot.janet

@@ -349,6 +349,13 @@
         "sort 5")
 (assert (<= ;(sort (map (fn [x] (math/random)) (range 1000)))) "sort 6")
 
+# #1283  
+(assert (deep=
+          (partition 2 (generate [ i :in [:a :b :c :d :e]] i))
+          '@[(:a :b) (:c :d) (:e)]))
+(assert (= (mean (generate [i :in [2 3 5 7 11]] i))
+           5.6))
+
 # And and or
 # c16a9d846
 (assert (= (and true true) true) "and true true")