From 4b56f22a2811412aa05a76a1e56171acc7341dee Mon Sep 17 00:00:00 2001
From: Kaz Kylheku <kaz@kylheku.com>
Date: Thu, 17 Aug 2023 07:15:55 -0700
Subject: New function: csort-group.

* autoload.c (csort_set_entries): Register csort-group
as autoload trigger for stdlib/csort.tl.

* stdlib/csort.tl (csort-group): New function.

* tests/012/sort.tl: Tests for sort-group and csort-group.

* txr.1: Documented.

* stdlib/doc-syms.tl: Updated.
---
 autoload.c         |  1 +
 stdlib/csort.tl    |  3 +++
 stdlib/doc-syms.tl |  3 ++-
 tests/012/sort.tl  | 10 ++++++++++
 txr.1              | 11 ++++++++++-
 5 files changed, 26 insertions(+), 2 deletions(-)

diff --git a/autoload.c b/autoload.c
index 417f6fb0..b251ae9e 100644
--- a/autoload.c
+++ b/autoload.c
@@ -960,6 +960,7 @@ static val csort_set_entries(val fun)
 {
   val name[] = {
     lit("csort"), lit("cnsort"), lit("cssort"), lit("csnsort"),
+    lit("csort-group"),
     nil
   };
   autoload_set(al_fun, name, fun);
diff --git a/stdlib/csort.tl b/stdlib/csort.tl
index 44715236..345b4ce8 100644
--- a/stdlib/csort.tl
+++ b/stdlib/csort.tl
@@ -41,3 +41,6 @@
 
 (defun csnsort (seq : (less-fun :) (key-fun :))
   (cached-sort-body snsort))
+
+(defun csort-group (seq : (key-fun :) (less-fun :))
+  (partition-by key-fun (csort seq less-fun key-fun)))
diff --git a/stdlib/doc-syms.tl b/stdlib/doc-syms.tl
index f3d793d2..edde5200 100644
--- a/stdlib/doc-syms.tl
+++ b/stdlib/doc-syms.tl
@@ -453,6 +453,7 @@
       ("csize" "N-01B1B5DF")
       ("csnsort" "N-02102493")
       ("csort" "N-02102493")
+      ("csort-group" "N-00CDF784")
       ("cssort" "N-02102493")
       ("cstopb" "N-01B1B5DF")
       ("cum-norm-dist" "N-03AB449B")
@@ -1920,7 +1921,7 @@
       ("some-false" "N-016BDF48")
       ("some-true" "N-016BDF48")
       ("sort" "N-03923640")
-      ("sort-group" "N-01E65DDC")
+      ("sort-group" "N-00CDF784")
       ("source-loc" "N-0370CD69")
       ("source-loc-str" "N-0370CD69")
       ("span-str" "N-0394CA3A")
diff --git a/tests/012/sort.tl b/tests/012/sort.tl
index 4989a74b..03c122d3 100644
--- a/tests/012/sort.tl
+++ b/tests/012/sort.tl
@@ -78,3 +78,13 @@
     (cssort svec) vec
     (cssort vec (fun greater)) (reverse vec)
     (cssort svec (fun greater)) (reverse vec)))
+
+(mtest
+  [sort-group '((a 1) (b 1) (a 2) (b 2) (a 3) (c 2) (c 1) (a 4)) car]
+  (((a 1) (a 2) (a 3) (a 4))
+   ((b 1) (b 2))
+   ((c 2) (c 1)))
+  [csort-group '((a 1) (b 1) (a 2) (b 2) (a 3) (c 2) (c 1) (a 4)) car]
+  (((a 1) (a 2) (a 3) (a 4))
+   ((b 1) (b 2))
+   ((c 2) (c 1))))
diff --git a/txr.1 b/txr.1
index f41337c0..6e61c412 100644
--- a/txr.1
+++ b/txr.1
@@ -38372,7 +38372,7 @@ has the same effect as:
   -> "uryyb, jbeyq!"
 .brev
 
-.coNP Function @ sort-group
+.coNP Functions @ sort-group and @ csort-group
 .synb
 .mets (sort-group < sequence >> [ keyfun <> [ lessfun ]])
 .syne
@@ -38389,6 +38389,15 @@ arguments, and then breaks the resulting sequence into groups,
 based on the equivalence of the elements under
 .metn keyfun .
 
+The
+.code csort-group
+differs from
+.code sort-group
+in that it is based on the caching
+.code csort
+rather than
+.codn sort .
+
 The following equivalence holds:
 
 .verb
-- 
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