math.statistics: adding z-score.

basis/math/statistics/statistics-docs.factor

@@ -267,6 +267,10 @@ HELP: collect-index-by
     }
 } ;
 
+HELP: z-score
+{ $values { "seq" sequence } { "n" number } }
+{ $description "Calculates the Z-Score for " { $snippet "seq" } "." } ;
+
 ARTICLE: "histogram" "Computing histograms"
 "Counting elements in a sequence:"
 { $subsections

basis/math/statistics/statistics.factor

@@ -388,3 +388,6 @@ ALIAS: std sample-std
         [ values ] map [ 0 [ length + ] accumulate nip ] [ ] bi zip
     ] [ length f <array> ] bi
     [ '[ first2 [ _ set-nth ] with each ] each ] keep ;
+
+: z-score ( seq -- n )
+    dup [ mean ] [ sample-std ] bi '[ _ - _ / ] map ;