Enhance seq-min and seq-max (was: stream.el)

[Michael Heerdegen]

Nicolas Petton <address@hidden> writes:

> It's ok to fix them, but I'd like to stay involved at least.

Ok, great.

I would like to extend seq-min and seq-max to allow (a) arbitrary
comparison functions and (b) key functions like in cl, so that you can
find e.g. the longest string in a sequence of strings.  I miss this
functionality, AFAIK cl-lib also can't do it.

Like this, maybe?

From 3cbaf1316de41687a6a3a6d67e4cc773769999c3 Mon Sep 17 00:00:00 2001
From: Michael Heerdegen <address@hidden>
Date: Fri, 10 May 2019 15:08:57 +0200
Subject: [PATCH] WIP: Enhance seq-min and seq-max

---
 lisp/emacs-lisp/seq.el | 34 +++++++++++++++++++++++++++-------
 1 file changed, 27 insertions(+), 7 deletions(-)

diff --git a/lisp/emacs-lisp/seq.el b/lisp/emacs-lisp/seq.el
index 3413cd1513..ddd8f3161c 100644
--- a/lisp/emacs-lisp/seq.el
+++ b/lisp/emacs-lisp/seq.el
@@ -451,15 +451,35 @@ seq-group-by
    (seq-reverse sequence)
    nil))

-(cl-defgeneric seq-min (sequence)
+(cl-defgeneric seq-min (sequence &optional predicate key)
   "Return the smallest element of SEQUENCE.
-SEQUENCE must be a sequence of numbers or markers."
-  (apply #'min (seq-into sequence 'list)))
-
-(cl-defgeneric seq-max (sequence)
+With PREDICATE given, use it to compare elements.  The default is
+`<'.
+With function KEY given, call it on the individual elements and
+compare the results instead of the elements."
+  (if predicate
+      (seq-reduce
+       (if key
+           (lambda (x y)
+             (if (funcall predicate (funcall key y) (funcall key x)) y x))
+         (lambda (x y) (if (funcall predicate y x) y x)))
+       sequence (car sequence))
+    (apply #'min (seq-into sequence 'list))))
+
+(cl-defgeneric seq-max (sequence &optional predicate key)
   "Return the largest element of SEQUENCE.
-SEQUENCE must be a sequence of numbers or markers."
-  (apply #'max (seq-into sequence 'list)))
+With PREDICATE given, use it to compare elements.  The default is
+`<'.
+With function KEY given, call it on the individual elements and
+compare the results instead of the elements."
+  (if predicate
+      (seq-reduce
+       (if key
+           (lambda (x y)
+             (if (funcall predicate (funcall key x) (funcall key y)) y x))
+         (lambda (x y) (if (funcall predicate x y) y x)))
+       sequence (car sequence))
+    (apply #'max (seq-into sequence 'list))))

 (defun seq--count-successive (pred sequence)
   "Return the number of successive elements for which (PRED element) is 
non-nil in SEQUENCE."
--
2.20.1

I made it so that if the result is ambiguous (e.g. multiple strings with
equal length), the first one is returned, but that is not explicitly
documented.

Regards,

Michael.