up

benford.rkt

@@ -0,0 +1,37 @@
+#lang typed/racket
+(define (freq l)
+  (define h (make-vector 10 0))
+  (define tot
+    (for/fold ([tot 0]) ([e (in-list l)])
+      (dict-update! h e add1)
+      (add1 tot)))
+  (for/list ([(e c) (in-dict h)])
+    (cons e (/ c tot))))
+(define nums->digits
+  (curry map
+         (compose string->number
+                  string
+                  (λ (x) (string-ref x 0))
+                  number->string
+                  (λ (x) (if (x . < . 0) (- x) x)))))
+(define (sk l)
+  (freq (nums->digits l)))
+(define (sort-em l)
+  (sort l >= #:key cdr))
+
+(equal?
+ (sort-em
+  (sk (list 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 0.10
+            11 12 13 -14 15 16 17 18 19
+            21 -22 23 24 25 26 27 28
+            31 32 -33 34 35 36 37
+            41 42 43 44 45 46
+            51 -52 54 54 55
+            61 62 -63 64
+            71 -72 73
+            81 82
+            91)))
+ (for/list ([i (in-range 10)])
+   (cons i
+         (/ (- 10 i)
+            (+ 10 9 8 7 6 5 4 3 2 1)))))