September 2017 Update

Task/Sort-an-array-of-composite-structures/JavaScript/sort-an-array-of-composite-structures-2.js

@@ -0,0 +1,62 @@
+(() => {
+    'use strict';
+
+    // GENERIC FUNCTIONS FOR COMPARISONS
+
+    // compare :: a -> a -> Ordering
+    const compare = (a, b) => a < b ? -1 : (a > b ? 1 : 0);
+
+    // on :: (b -> b -> c) -> (a -> b) -> a -> a -> c
+    const on = (f, g) => (a, b) => f(g(a), g(b));
+
+    // flip :: (a -> b -> c) -> b -> a -> c
+    const flip = f => (a, b) => f.apply(null, [b, a]);
+
+    // arrayCopy :: [a] -> [a]
+    const arrayCopy = (xs) => xs.slice(0);
+
+    // show :: a -> String
+    const show = x => JSON.stringify(x, null, 2);
+
+
+    // TEST
+    const xs = [{
+        name: 'Shanghai',
+        pop: 24.2
+    }, {
+        name: 'Karachi',
+        pop: 23.5
+    }, {
+        name: 'Beijing',
+        pop: 21.5
+    }, {
+        name: 'Sao Paulo',
+        pop: 24.2
+    }, {
+        name: 'Dhaka',
+        pop: 17.0
+    }, {
+        name: 'Delhi',
+        pop: 16.8
+    }, {
+        name: 'Lagos',
+        pop: 16.1
+    }]
+
+    // population :: Dictionary -> Num
+    const population = x => x.pop;
+
+    // name :: Dictionary -> String
+    const name = x => x.name;
+
+    return show({
+        byPopulation: arrayCopy(xs)
+            .sort(on(compare, population)),
+        byDescendingPopulation: arrayCopy(xs)
+            .sort(on(flip(compare), population)),
+        byName: arrayCopy(xs)
+            .sort(on(compare, name)),
+        byDescendingName: arrayCopy(xs)
+            .sort(on(flip(compare), name))
+    });
+})();