math.statistics: adding a normalized-histogram word.

basis/math/statistics/statistics-tests.factor

@@ -77,6 +77,9 @@ IN: math.statistics.tests
     "aabbcc" histogram
 ] unit-test
 
+{ H{ { 1 1/2 } { 2 1/6 } { 3 1/3 } } }
+[ { 1 1 1 1 1 1 2 2 3 3 3 3 } normalized-histogram ] unit-test
+
 {
     V{ 0 3 6 9 }
     V{ 1 4 7 }

basis/math/statistics/statistics.factor

@@ -227,6 +227,9 @@ PRIVATE>
 : sorted-histogram ( seq -- alist )
     histogram sort-values ;
 
+: normalized-histogram ( seq -- alist )
+    [ histogram ] [ length ] bi '[ _ / ] assoc-map ;
+
 : collect-pairs ( seq quot: ( x -- v k ) -- hashtable )
     [ push-at ] sequence>hashtable ; inline