From 001a12d166ab0afeb771c2bd89d7bd34fac4f193 Mon Sep 17 00:00:00 2001
From: Sergiu Ivanov <sivanov@colimite.fr>
Date: Mon, 22 May 2023 15:34:27 +0200
Subject: [PATCH] Type group-truth-table-by-nai.

---
 scribblings/tbn.scrbl | 20 ++++++++++++++++++++
 tbn.rkt               | 28 ++++++++++++++++++++++++++++
 2 files changed, 48 insertions(+)

diff --git a/scribblings/tbn.scrbl b/scribblings/tbn.scrbl
index 1e575d6..a6654ff 100644
--- a/scribblings/tbn.scrbl
+++ b/scribblings/tbn.scrbl
@@ -276,3 +276,23 @@ Like @racket[tabulate-tbfs/state] and
 (tabulate-tbf/state (tbf/state (hash 'a 1 'b 2) 2))
 (tabulate-tbf/state+headers (tbf/state (hash 'a 1 'b 2) 2))
 ]}
+
+@section{Miscellaneous utilities}
+
+@defproc[(group-truth-table-by-nai [tt (Listof (Listof Integer))])
+				   (Listof (Listof (Listof Integer)))]{
+
+Given the truth table @racket[tt] of a Boolean function, groups the
+lines by the @italic{N}umber of @italic{A}ctivated @italic{I}nputs—the
+number of inputs which are 1 in the input vector.
+
+@ex[
+(group-truth-table-by-nai '((0 0 0 1)
+                            (0 0 1 1)
+                            (0 1 0 0)
+                            (0 1 1 1)
+                            (1 0 0 0)
+                            (1 0 1 0)
+                            (1 1 0 1)
+                            (1 1 1 0)))
+]}
diff --git a/tbn.rkt b/tbn.rkt
index f8a782f..286b69b 100644
--- a/tbn.rkt
+++ b/tbn.rkt
@@ -32,6 +32,8 @@
 
    tabulate-tbfs/state tabulate-tbfs/state+headers
    tabulate-tbf/state tabulate-tbf/state+headers
+
+   group-truth-table-by-nai
    )
 
   (: apply-tbf-to-state (-> TBF (State (U Zero One)) (U Zero One)))
@@ -289,6 +291,32 @@
                       (0 1 0)
                       (1 0 0)
                       (1 1 1)))))
+
+  (: group-truth-table-by-nai (-> (Listof (Listof Integer))
+                                  (Listof (Listof (Listof Integer)))))
+  (define (group-truth-table-by-nai tt)
+    (: sum (-> (Listof Integer) Integer))
+    (define (sum xs) (foldl + 0 xs))
+    (group-by (λ ([row : (Listof Integer)])
+                (drop-right row 1))
+              tt
+              (λ ([in1 : (Listof Integer)] [in2 : (Listof Integer)])
+                (= (sum in1) (sum in2)))))
+
+  (module+ test
+    (test-case "group-truth-table-by-nai"
+      (check-equal? (group-truth-table-by-nai '((0 0 0 1)
+                                                (0 0 1 1)
+                                                (0 1 0 0)
+                                                (0 1 1 1)
+                                                (1 0 0 0)
+                                                (1 0 1 0)
+                                                (1 1 0 1)
+                                                (1 1 1 0)))
+                    '(((0 0 0 1))
+                      ((0 0 1 1) (0 1 0 0) (1 0 0 0))
+                      ((0 1 1 1) (1 0 1 0) (1 1 0 1))
+                      ((1 1 1 0))))))
   )
 
 (module+ test