Add _.sortedLastIndex

Closes jashkenas#1882.
jridgewell · Mar 13, 2015 · 97a7d25 · 97a7d25
1 parent f77e099
commit 97a7d25
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Showing 2 changed files with 47 additions and 12 deletions.
diff --git a/test/arrays.js b/test/arrays.js
@@ -112,9 +112,9 @@
   });
 
   test('sortedIndex', function() {
-    var numbers = [10, 20, 30, 40, 50], num = 35;
+    var numbers = [10, 20, 30, 30, 30, 40, 50], num = 35;
     var indexForNum = _.sortedIndex(numbers, num);
-    equal(indexForNum, 3, '35 should be inserted at index 3');
+    equal(indexForNum, 5, '35 should be inserted at index 5');
 
     var indexFor30 = _.sortedIndex(numbers, 30);
     equal(indexFor30, 2, '30 should be inserted at index 2');
@@ -137,6 +137,32 @@
     equal(_.sortedIndex(array, 2147483648), 2147483648, 'should work with large indexes');
   });
 
+  test('sortedLastIndex', function() {
+    var numbers = [10, 20, 30, 30, 30, 40, 50], num = 35;
+    var indexForNum = _.sortedLastIndex(numbers, num);
+    equal(indexForNum, 5, '35 should be inserted at index 5');
+
+    var indexFor30 = _.sortedLastIndex(numbers, 30);
+    equal(indexFor30, 5, '30 should be inserted at index 5');
+
+    var objects = [{x: 10}, {x: 20}, {x: 30}, {x: 40}];
+    var iterator = function(obj){ return obj.x; };
+    strictEqual(_.sortedLastIndex(objects, {x: 25}, iterator), 2);
+    strictEqual(_.sortedLastIndex(objects, {x: 35}, 'x'), 3);
+
+    var context = {1: 2, 2: 3, 3: 4};
+    iterator = function(obj){ return this[obj]; };
+    strictEqual(_.sortedLastIndex([1, 3], 2, iterator, context), 1);
+
+    var values = [0, 1, 3, 7, 15, 31, 63, 127, 255, 511, 1023, 2047, 4095, 8191, 16383, 32767, 65535, 131071, 262143, 524287, 1048575, 2097151, 4194303, 8388607, 16777215, 33554431, 67108863, 134217727, 268435455, 536870911, 1073741823, 2147483647];
+    var array = Array(Math.pow(2, 32) - 1);
+    var length = values.length;
+    while (length--) {
+      array[values[length]] = values[length];
+    }
+    equal(_.sortedLastIndex(array, 2147483648), 2147483648, 'should work with large indexes');
+  });
+
   test('uniq', function() {
     var list = [1, 2, 1, 3, 1, 4];
     deepEqual(_.uniq(list), [1, 2, 3, 4], 'can find the unique values of an unsorted array');

diff --git a/underscore.js b/underscore.js
@@ -655,16 +655,25 @@
 
   // Use a comparator function to figure out the smallest index at which
   // an object should be inserted so as to maintain order. Uses binary search.
-  _.sortedIndex = function(array, obj, iteratee, context) {
-    iteratee = cb(iteratee, context, 1);
-    var value = iteratee(obj);
-    var low = 0, high = array.length;
-    while (low < high) {
-      var mid = Math.floor((low + high) / 2);
-      if (iteratee(array[mid]) < value) low = mid + 1; else high = mid;
-    }
-    return low;
-  };
+  function createSortedIndexFinder(lessThan) {
+    return function(array, obj, iteratee, context) {
+      iteratee = cb(iteratee, context, 1);
+      var value = iteratee(obj);
+      var low = 0, high = array.length;
+      while (low < high) {
+        var mid = Math.floor((low + high) / 2);
+        var computed = iteratee(array[mid]);
+        if ((lessThan && computed < value) || (!lessThan && computed <= value)) {
+          low = mid + 1;
+        } else {
+          high = mid;
+        }
+      }
+      return low;
+    };
+  }
+  _.sortedIndex = createSortedIndexFinder(true);
+  _.sortedLastIndex = createSortedIndexFinder(false);
 
   // Generate an integer Array containing an arithmetic progression. A port of
   // the native Python `range()` function. See