Add minmax to comparisons (#21820)

* Add `minmax` to sequtils

This adds a `minmax` proc to complement `min` and `max`; it computes
both results in a single pass for efficiency.

* Update lib/pure/collections/sequtils.nim

* Add minmax note to changelog.

---------

Co-authored-by: Andreas Rumpf <rumpf_a@web.de>

changelogs/changelog_2_0_0.md

@@ -305,6 +305,7 @@
 - Added `openArray[char]` overloads for `std/unicode` allowing more code reuse.
 - Added `safe` parameter to `base64.encodeMime`.
 - Added `parseutils.parseSize` - inverse to `strutils.formatSize` - to parse human readable sizes.
+- Added `minmax` to `sequtils`, as a more efficient `(min(_), max(_))` over sequences.
 
 [//]: # "Deprecations:"
 - Deprecated `selfExe` for Nimscript.

lib/pure/collections/sequtils.nim

@@ -248,6 +248,15 @@ func maxIndex*[T](s: openArray[T]): int {.since: (1, 1).} =
   for i in 1..high(s):
     if s[i] > s[result]: result = i
 
+func minmax*[T](x: openArray[T]): (T, T) =
+  ## The minimum and maximum values of `x`. `T` needs to have a `<` operator.
+  var l = x[0]
+  var h = x[0]
+  for i in 1..high(x):
+    if x[i] < l: l = x[i]
+    if h < x[i]: h = x[i]
+  result = (l, h)
+
 
 template zipImpl(s1, s2, retType: untyped): untyped =
   proc zip*[S, T](s1: openArray[S], s2: openArray[T]): retType =

tests/collections/tseq.nim

@@ -12,6 +12,7 @@ FilterIt: [1, 3, 7]
 Concat: [1, 3, 5, 7, 2, 4, 6]
 Deduplicate: [1, 2, 3, 4, 5, 7]
 @[()]
+Minmax: (1, 7)
 2345623456
 '''
 """
@@ -156,6 +157,13 @@ block tsequtils:
   let someObjSeq = aSeq.mapIt(it.field)
   echo someObjSeq
 
+  block minmax:
+    doAssert minmax(@[0]) == (0, 0)
+    doAssert minmax(@[0, 1]) == (0, 1)
+    doAssert minmax(@[1, 0]) == (0, 1)
+    doAssert minmax(@[8,2,1,7,3,9,4,0,5]) == (0, 9)
+    echo "Minmax: ", $(minmax(concat(seq1, seq2)))
+
 
 when not defined(nimseqsv2):
   block tshallowseq: