* eval.c (eval_init): Register sort-group.

* lib.c (sort_group): New function.

* lib.h (sort_group): Declared.

* txr.1: Documented.

5 files changed, 53 insertions, 1 deletions

diff --git a/ChangeLog b/ChangeLog
index 932dc26c..ee5a3e17 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,5 +1,15 @@
 2014-11-21  Kaz Kylheku  <kaz@kylheku.com>
 
+	* eval.c (eval_init): Register sort-group.
+
+	* lib.c (sort_group): New function.
+
+	* lib.h (sort_group): Declared.
+
+	* txr.1: Documented.
+
+2014-11-21  Kaz Kylheku  <kaz@kylheku.com>
+
 	* lib.c (partition_star_func): Bugfix: doing rplaca(env, seq)
 	too early, before the loop which adjusts its value.
 	Restructuring this slightly to avoid duplicated code, by moving the
diff --git a/eval.c b/eval.c
index ef9b5cd7..1a1fb0c2 100644
--- a/eval.c
+++ b/eval.c
@@ -3774,6 +3774,7 @@ void eval_init(void)
   reg_fun(intern(lit("hash-diff"), user_package), func_n2(hash_diff));
   reg_fun(intern(lit("hash-isec"), user_package), func_n3o(hash_isec, 2));
   reg_fun(intern(lit("group-by"), user_package), func_n2v(group_by));
+  reg_fun(intern(lit("sort-group"), user_package), func_n3o(sort_group, 1));
   reg_fun(intern(lit("uniq"), user_package), func_n1(uniq));
   reg_fun(intern(lit("hash-update"), user_package), func_n2(hash_update));
   reg_fun(intern(lit("hash-update-1"), user_package),
diff --git a/lib.c b/lib.c
index 53f645ef..13c9d388 100644
--- a/lib.c
+++ b/lib.c
@@ -5695,6 +5695,15 @@ val multi_sort(val lists, val funcs, val key_funcs)
   return mapcarv(list_f, tuples);
 }
 
+val sort_group(val seq, val keyfun, val lessfun)
+{
+  val kf = default_arg(keyfun, identity_f);
+  val lf = default_arg(lessfun, less_f);
+  val seq_copy = copy(seq);
+  val sorted = sort(seq_copy, lf, kf);
+  return partition_by(kf, sorted);
+}
+
 val uniq(val seq)
 {
   val hash = make_hash(nil, nil, t);
@@ -5727,7 +5736,6 @@ val uniq(val seq)
   return make_like(out, seq);
 }
 
-
 val find(val item, val list, val testfun, val keyfun)
 {
   testfun = default_arg(testfun, equal_f);
diff --git a/lib.h b/lib.h
index c5c187ff..03a972fa 100644
--- a/lib.h
+++ b/lib.h
@@ -796,6 +796,7 @@ val interpose(val sep, val seq);
 val merge(val list1, val list2, val lessfun, val keyfun);
 val sort(val seq, val lessfun, val keyfun);
 val multi_sort(val lists, val funcs, val key_funcs);
+val sort_group(val seq, val keyfun, val lessfun);
 val uniq(val seq);
 val find(val list, val key, val testfun, val keyfun);
 val find_if(val pred, val list, val key);
diff --git a/txr.1 b/txr.1
index 8c950bad..a9b2d138 100644
--- a/txr.1
+++ b/txr.1
@@ -17676,6 +17676,38 @@ For strings and vectors,
 .code sort
 is not stable.
 
+.coNP Function sort-group
+.synb
+.mets (sort-group < sequence >> [ keyfun <> [ lessfun ]])
+.syne
+.desc
+The
+.code sort-group
+function sorts
+.meta sequence
+according to the
+.meta keyfun
+and
+.meta lessfun
+arguments, and then breaks the resulting sequence into groups,
+based on the equivalence of the elements under
+.metn keyfun .
+
+The following equivalence holds:
+
+.cblk
+  (sort-group sq lf kf) <--> (partition-by kf (sort (copy sq) kf lf))
+.cble
+
+Note the reversed order of
+.meta keyfun
+and
+.meta lessfun
+arguments between
+.code sort
+and
+.codn sort-group .
+
 .coNP Function @ uniq
 .synb
 .mets (uniq << sequence )