Merge branch 'master' of factorcode.org:/git/factor

core/sorting/sorting-docs.factor

@@ -3,6 +3,10 @@ sequences math.order ;
 IN: sorting
 
 ARTICLE: "sequences-sorting" "Sorting sequences"
+"The " { $vocab-link "sorting" } " vocabulary implements the merge-sort algorithm. It runs in " { $snippet "O(n log n)" } " time, and is a " { $emphasis "stable" } " sort, meaning that the order of equal elements is preserved."
+$nl
+"The algorithm only allocates two additional arrays, both the size of the input sequence, and uses iteration rather than recursion, and thus is suitable for sorting large sequences."
+$nl
 "Sorting combinators all take comparator quotations with stack effect " { $snippet "( elt1 elt2 -- <=> )" } ", where the output value is one of the three " { $link "order-specifiers" } "."
 $nl
 "Sorting a sequence with a custom comparator:"

core/sorting/sorting-tests.factor

@@ -18,3 +18,9 @@ unit-test
 ] unit-test
 
 [ ] [ { 1 2 } [ 2drop 1 ] sort drop ] unit-test
+
+! Is it a stable sort?
+[ t ] [ { { 1 "a" } { 1 "b" } { 1 "c" } } dup sort-keys = ] unit-test
+
+[ { { 1 "a" } { 1 "b" } { 1 "c" } { 1 "e" } { 2 "d" } } ]
+[ { { 1 "a" } { 1 "b" } { 1 "c" } { 2 "d" } { 1 "e" } } sort-keys ] unit-test

core/sorting/sorting.factor

@@ -24,11 +24,23 @@ TUPLE: merge
 { to2    array-capacity } ;
 
 : dump ( from to seq accum -- )
-    #! Optimize common case where to - from = 1.
+    #! Optimize common case where to - from = 1, 2, or 3.
-    >r >r 2dup swap - 1 =
+    >r >r 2dup swap - dup 1 =
-    [ drop r> nth-unsafe r> push ]
+    [ 2drop r> nth-unsafe r> push ] [
-    [ r> <slice> r> push-all ]
+        dup 2 = [
-    if ; inline
+            2drop dup 1+
+            r> [ nth-unsafe ] curry bi@
+            r> [ push ] curry bi@
+        ] [
+            dup 3 = [
+                2drop dup 1+ dup 1+
+                r> [ nth-unsafe ] curry tri@
+                r> [ push ] curry tri@
+            ] [
+                drop r> subseq r> push-all
+            ] if
+        ] if
+    ] if ; inline
 
 : l-elt   [ from1>> ] [ seq>> ] bi nth-unsafe ; inline
 : r-elt   [ from2>> ] [ seq>> ] bi nth-unsafe ; inline
@@ -38,13 +50,13 @@ TUPLE: merge
 : dump-r  [ [ from2>> ] [ to2>> ] [ seq>> ] tri ] [ accum>> ] bi dump ; inline
 : l-next  [ [ l-elt ] [ [ 1+ ] change-from1 drop ] bi ] [ accum>> ] bi push ; inline
 : r-next  [ [ r-elt ] [ [ 1+ ] change-from2 drop ] bi ] [ accum>> ] bi push ; inline
-: decide  [ [ l-elt ] [ r-elt ] bi ] dip call +lt+ eq? ; inline
+: decide  [ [ l-elt ] [ r-elt ] bi ] dip call +gt+ eq? ; inline
 
 : (merge) ( merge quot -- )
-    over l-done? [ drop dump-r ] [
+    over r-done? [ drop dump-l ] [
-        over r-done? [ drop dump-l ] [
+        over l-done? [ drop dump-r ] [
             2dup decide
-            [ over l-next ] [ over r-next ] if
+            [ over r-next ] [ over l-next ] if
             (merge)
         ] if
     ] if ; inline

extra/usa-cities/usa-cities.factor

@@ -2,7 +2,7 @@
 ! See http://factorcode.org/license.txt for BSD license.
 USING: io.files io.encodings.ascii sequences generalizations
 math.parser combinators kernel memoize csv symbols summary
-words accessors math.order sorting ;
+words accessors math.order binary-search ;
 IN: usa-cities
 
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