Travis build: 1378

README.md

@@ -138,6 +138,7 @@ average(1, 2, 3);
 * [`shuffle`](#shuffle)
 * [`similarity`](#similarity)
 * [`sortedIndex`](#sortedindex)
+* [`sortedLastIndex`](#sortedlastindex)
 * [`symmetricDifference`](#symmetricdifference)
 * [`symmetricDifferenceBy`](#symmetricdifferenceby)
 * [`symmetricDifferenceWith`](#symmetricdifferencewith)
@@ -1801,6 +1802,37 @@ sortedIndex([30, 50], 40); // 1
 <br>[⬆ Back to top](#table-of-contents)
 
 
+### sortedLastIndex
+
+Returns the highest index at which value should be inserted into array in order to maintain its sort order.
+
+Check if the array is sorted in descending order (loosely).
+Use `Array.map()` to map each element to an array with its index and value.
+Use `Array.filter()` to find all possible positions where the element could be inserted, `Array.slice(-1)` to get the last one.
+
+```js
+const sortedLastIndex = (arr, n) => {
+  const isDescending = arr[0] > arr[arr.length - 1];
+  const index = arr
+    .map((val, i) => [i, val])
+    .filter(el => (isDescending ? n >= el[1] : n >= el[1]))
+    .slice(-1)[0][0];
+  return index === -1 ? arr.length : index;
+};
+```
+
+<details>
+<summary>Examples</summary>
+
+```js
+sortedLastIndex([10, 20, 30, 30, 40], 30); // 3
+```
+
+</details>
+
+<br>[⬆ Back to top](#table-of-contents)
+
+
 ### symmetricDifference
 
 Returns the symmetric difference between two arrays.