2016 Update

Task/Greatest-element-of-a-list/JavaScript/greatest-element-of-a-list-2.js

@@ -1,59 +1,53 @@
 (function () {
 
-    // Generalised max() function
-    // [a] -> (a -> n) -> a
-    function max(list, fnCompare) {
-        return list.reduce(function (acc, b) {
-            var a = acc || b,
-                lngDiff = fnCompare(a, b);
-
-            return lngDiff ? (lngDiff > 0 ? b : a) : a;
-        }, null)
+    // (a -> a -> Ordering) -> [a] -> a
+    function maximumBy(f, xs) {
+        return xs.reduce(function (a, x) {
+            return a === undefined ? x : (
+                f(x, a) > 0 ? x : a
+            );
+        }, undefined);
     }
 
-    // Comparison functions for specific data types
+    // COMPARISON FUNCTIONS FOR SPECIFIC DATA TYPES
+
+    //Ordering: (LT|EQ|GT)
+    //  GT: 1 (or other positive n)
+    //  EQ: 0
+    //  LT: -1 (or other negative n)
 
     function wordSortFirst(a, b) {
-        return a === null ? b : a === b ? 0 : a < b ? -1 : 1;
+        return a < b ? 1 : (a > b ? -1 : 0)
     }
 
     function wordSortLast(a, b) {
-        return a === null ? b : a === b ? 0 : a < b ? 1 : -1;
+        return a < b ? -1 : (a > b ? 1 : 0)
     }
 
     function wordLongest(a, b) {
-        var lngA = a ? a.length : b.length,
-            lngB = b.length;
-
-        return lngA === lngB ? 0 : lngA > lngB ? -1 : 1;
+        return a.length - b.length;
     }
 
     function cityPopulationMost(a, b) {
-        var nA = a ? a.population : b.population,
-            nB = b.population;
-
-        return nA === nB ? 0 : nA > nB ? -1 : 1;
+        return a.population - b.population;
     }
 
     function cityPopulationLeast(a, b) {
-        var nA = a ? a.population : b.population,
-            nB = b.population;
-
-        return nA === nB ? 0 : nA < nB ? -1 : 1;
+        return b.population - a.population;
     }
 
     function cityNameSortFirst(a, b) {
-        var sA = a ? a.name : b.name,
-            sB = b.name;
+        var strA = a.name,
+            strB = b.name;
 
-        return sA === sB ? 0 : sA < sB ? -1 : 1;
+        return strA < strB ? 1 : (strA > strB ? -1 : 0);
     }
 
     function cityNameSortLast(a, b) {
-        var sA = a ? a.name : b.name,
-            sB = b.name;
+        var strA = a.name,
+            strB = b.name;
 
-        return sA === sB ? 0 : sA > sB ? -1 : 1;
+        return strA < strB ? -1 : (strA > strB ? 1 : 0);
     }
 
     var lstWords = [
@@ -62,38 +56,38 @@
         ];
 
     var lstCities = [
-            {
-                name: 'Shanghai',
-                population: 24.15
+        {
+            name: 'Shanghai',
+            population: 24.15
             }, {
-                name: 'Karachi',
-                population: 23.5
+            name: 'Karachi',
+            population: 23.5
             }, {
-                name: 'Beijing',
-                population: 21.5
+            name: 'Beijing',
+            population: 21.5
             }, {
-                name: 'Tianjin',
-                population: 14.7
+            name: 'Tianjin',
+            population: 14.7
             }, {
-                name: 'Istanbul',
-                population: 14.4
+            name: 'Istanbul',
+            population: 14.4
             }, , {
-                name: 'Lagos',
-                population: 13.4
+            name: 'Lagos',
+            population: 13.4
             }, , {
-                name: 'Tokyo',
-                population: 13.3
+            name: 'Tokyo',
+            population: 13.3
             }
         ];
 
     return [
-        max(lstWords, wordSortFirst),
-        max(lstWords, wordSortLast),
-        max(lstWords, wordLongest),
-        max(lstCities, cityPopulationMost),
-        max(lstCities, cityPopulationLeast),
-        max(lstCities, cityNameSortFirst),
-        max(lstCities, cityNameSortLast)
+        maximumBy(wordSortFirst, lstWords),
+        maximumBy(wordSortLast, lstWords),
+        maximumBy(wordLongest, lstWords),
+        maximumBy(cityPopulationMost, lstCities),
+        maximumBy(cityPopulationLeast, lstCities),
+        maximumBy(cityNameSortFirst, lstCities),
+        maximumBy(cityNameSortLast, lstCities)
     ]
 
 })();