fix(recall, precision): little bug in calculations

feat(fmeasure): calculate fmeasure using recall and precision

examples/naivebayes-doc-classifier.hs

@@ -24,6 +24,11 @@ module Main
       let showResults (c, r) = putStrLn (classes !! c ++ " ~ " ++ classes !! r)
       mapM_ showResults results
 
+      let showAccuracy (c, r) =
+            print $ genericLength (filter (\(h, j) -> h == j && h == c) results) / genericLength results
+      mapM_ showAccuracy results
+
       putStrLn $ "Recall: " ++ show (recall results) ++ "%"
       putStrLn $ "Precision: " ++ show (precision results) ++ "%"
+      putStrLn $ "F Measure: " ++ show (fmeasure (precision results) (recall results))
       putStrLn $ "Accuracy: " ++ show (accuracy results) ++ "%"

src/Sibe/NaiveBayes.hs

@@ -9,6 +9,7 @@ module Sibe.NaiveBayes
    accuracy,
    precision,
    recall,
+   fmeasure,
   )
   where
     import Data.List
@@ -74,24 +75,27 @@ module Sibe.NaiveBayes
       let correct = filter (uncurry (==)) results
       in round $ genericLength correct / genericLength results * 100
 
-    recall :: [(Int, Int)] -> Int
+    recall :: [(Int, Int)] -> Double
     recall results =
       let classes = ordNub (map fst results)
-          s = sum (map rec classes) / genericLength results
+          s = sum (map rec classes) / genericLength classes
-      in round $ s * 100
+      in s * 100
       where
         rec a =
           let t = genericLength $ filter (\(c, r) -> c == r && c == a) results
               y = genericLength $ filter (\(c, r) -> c == a) results
           in t / y
 
-    precision :: [(Int, Int)] -> Int
+    precision :: [(Int, Int)] -> Double
     precision results =
       let classes = ordNub (map fst results)
-          s = sum (map prec classes) / genericLength results
+          s = sum (map prec classes) / genericLength classes
-      in round $ s * 100
+      in s * 100
       where
         prec a =
           let t = genericLength $ filter (\(c, r) -> c == r && c == a) results
               y = genericLength $ filter (\(c, r) -> r == a) results
           in t / y
+
+    fmeasure :: Double -> Double -> Double
+    fmeasure r p = (2 * p * r) / (p + r)