Data commit

Task/Range-extraction/JavaScript/range-extraction-2.js

@@ -0,0 +1,64 @@
+(function () {
+    'use strict';
+
+    // rangeFormat :: [Int] -> String
+    var rangeFormat = function (xs) {
+        return splitBy(function (a, b) {
+                return b - a > 1;
+            }, xs)
+            .map(rangeString)
+            .join(',');
+    };
+
+    // rangeString :: [Int] -> String
+    var rangeString = function (xs) {
+        return xs.length > 2 ? [head(xs), last(xs)].map(show)
+            .join('-') : xs.join(',');
+    };
+
+    // GENERIC FUNCTIONS
+
+    // Splitting not on a delimiter, but whenever the relationship between
+    // two consecutive items matches a supplied predicate function
+
+    // splitBy :: (a -> a -> Bool) -> [a] -> [[a]]
+    var splitBy = function (f, xs) {
+        if (xs.length < 2) return [xs];
+        var h = head(xs),
+            lstParts = xs.slice(1)
+            .reduce(function (a, x) {
+                var acc = a[0],
+                    active = a[1],
+                    prev = a[2];
+
+                return f(prev, x) ? (
+                    [acc.concat([active]), [x], x]
+                ) : [acc, active.concat(x), x];
+            }, [
+                [],
+                [h], h
+            ]);
+        return lstParts[0].concat([lstParts[1]]);
+    };
+
+    // head :: [a] -> a
+    var head = function (xs) {
+        return xs.length ? xs[0] : undefined;
+    };
+
+    // last :: [a] -> a
+    var last = function (xs) {
+        return xs.length ? xs.slice(-1)[0] : undefined;
+    };
+
+    // show :: a -> String
+    var show = function (x) {
+        return JSON.stringify(x);
+    };
+
+    // TEST
+    return rangeFormat([0, 1, 2, 4, 6, 7, 8, 11, 12, 14, 15, 16,
+        17, 18, 19, 20, 21, 22, 23, 24, 25, 27, 28, 29, 30, 31, 32,
+        33, 35, 36, 37, 38, 39
+    ]);
+})();