Better implementation of sample, fix docs formatting

basis/random/random-docs.factor

@@ -86,8 +86,9 @@ HELP: sample
 }
 { $description "Takes " { $snippet "n" } " samples at random without replacement from a sequence. Throws an error if " { $snippet "n" } " is longer than the sequence." }
 { $examples
-    { $unchecked-example "USING: random prettyprint ; { 1 2 3 } 2 sample ."
-        "{ 3 2 }"
+    { $unchecked-example "USING: random prettyprint ;"
+    "{ 1 2 3 } 2 sample ."
+    "{ 3 2 }"
     }
 } ;
 

basis/random/random.factor

@@ -61,29 +61,20 @@ M: sequence random
 
 : random-32 ( -- n ) random-generator get random-32* ;
 
-: randomize ( seq -- seq )
-    dup length [ dup 1 > ]
+: randomize-n-last ( seq n -- seq ) 
+    [ dup length dup ] dip - 1 max '[ dup _ > ] 
     [ [ random ] [ 1 - ] bi [ pick exchange ] keep ]
     while drop ;
 
+: randomize ( seq -- seq ) 
+    dup length randomize-n-last ;
+
 ERROR: too-many-samples seq n ;
 
-<PRIVATE
-
-:: next-sample ( length n seq hashtable -- elt )
-    n hashtable key? [
-        length n 1 + length mod seq hashtable next-sample
-    ] [
-        n hashtable conjoin
-        n seq nth
-    ] if ;
-
-PRIVATE>
-
 : sample ( seq n -- seq' )
     2dup [ length ] dip < [ too-many-samples ] when
-    swap [ length ] [ ] bi H{ } clone 
-    '[ _ dup random _ _ next-sample ] replicate ;
+    [ [ length iota >array ] dip [ randomize-n-last ] keep tail-slice* ]
+    [ drop ] 2bi nths ;
 
 : delete-random ( seq -- elt )
     [ length random-integer ] keep [ nth ] 2keep remove-nth! drop ;