# HG changeset patch
# User Steve Losh <steve@stevelosh.com>
# Date 1484845514 0
# Node ID 5dd997c404247dee64556b99c6f5d69ffde26d12
# Parent  fbd9837856a842beb9fb7696a2d0ce1c5c093b65
Add `extrema`

diff -r fbd9837856a8 -r 5dd997c40424 DOCUMENTATION.markdown
--- a/DOCUMENTATION.markdown	Tue Jan 17 21:33:28 2017 +0000
+++ b/DOCUMENTATION.markdown	Thu Jan 19 17:05:14 2017 +0000
@@ -1403,6 +1403,19 @@
 
   
 
+### `EXTREMA` (function)
+
+    (EXTREMA PREDICATE SEQUENCE)
+
+Return the smallest and largest elements of `sequence` according to `predicate`
+
+  `predicate` should be a strict ordering predicate (e.g. `<`).
+
+  Returns the smallest and largest elements in the sequence as two values,
+  respectively.
+
+  
+
 ### `FREQUENCIES` (function)
 
     (FREQUENCIES SEQUENCE &KEY (TEST 'EQL))
diff -r fbd9837856a8 -r 5dd997c40424 losh.lisp
--- a/losh.lisp	Tue Jan 17 21:33:28 2017 +0000
+++ b/losh.lisp	Thu Jan 19 17:05:14 2017 +0000
@@ -1676,6 +1676,23 @@
     (sequence (drop-seq n seq))))
 
 
+(defun extrema (predicate sequence)
+  "Return the smallest and largest elements of `sequence` according to `predicate`
+
+  `predicate` should be a strict ordering predicate (e.g. `<`).
+
+  Returns the smallest and largest elements in the sequence as two values,
+  respectively.
+
+  "
+  (iterate (with min = (elt sequence 0))
+           (with max = (elt sequence 0))
+           (for el :in-whatever sequence)
+           (when (funcall predicate el min) (setf min el))
+           (when (funcall predicate max el) (setf max el))
+           (finally (return (values min max)))))
+
+
 ;;;; Debugging & Logging ------------------------------------------------------
 (defun pr (&rest args)
   "Print `args` readably, separated by spaces and followed by a newline.
diff -r fbd9837856a8 -r 5dd997c40424 package.lisp
--- a/package.lisp	Tue Jan 17 21:33:28 2017 +0000
+++ b/package.lisp	Thu Jan 19 17:05:14 2017 +0000
@@ -241,6 +241,7 @@
 (defpackage :losh.sequences
   (:documentation "Utilities for operating on sequences.")
   (:export
+    :extrema
     :prefix-sums
     :frequencies
     :proportions