diff --git a/lodash.js b/lodash.js
index fae6f2d47..dc2671e58 100644
--- a/lodash.js
+++ b/lodash.js
@@ -646,42 +646,6 @@
     return false;
   }
 
-  /**
-   * Assigns `value` to `key` of `object` if the existing value is not equivalent
-   * using [`SameValueZero`](http://ecma-international.org/ecma-262/6.0/#sec-samevaluezero)
-   * for equality comparisons.
-   *
-   * @private
-   * @param {Object} object The object to modify.
-   * @param {string} key The key of the property to assign.
-   * @param {*} value The value to assign.
-   */
-  function assignValue(object, key, value) {
-    var oldValue = object[key];
-    if ((value === value ? (value !== oldValue) : (oldValue === oldValue)) ||
-        (value === undefined && !(key in object))) {
-      object[key] = value;
-    }
-  }
-
-  /**
-   * This function is like `assignValue` except that it doesn't assign `undefined` values.
-   *
-   * @private
-   * @param {Object} object The object to modify.
-   * @param {string} key The key of the property to assign.
-   * @param {*} value The value to assign.
-   */
-  function assignMergeValue(object, key, value) {
-    var oldValue = object[key];
-    if ((value !== undefined &&
-          (value === value ? (value !== oldValue) : (oldValue === oldValue))) ||
-        (typeof key == 'number' &&
-          value === undefined && !(key in object))) {
-      object[key] = value;
-    }
-  }
-
   /**
    * The base implementation of methods like `_.max` and `_.min` which accepts a
    * `comparator` to determine the extremum value.
@@ -1038,64 +1002,6 @@
     return object.index - other.index;
   }
 
-  /**
-   * Copies the values of `source` to `array`.
-   *
-   * @private
-   * @param {Array} source The array to copy values from.
-   * @param {Array} [array=[]] The array to copy values to.
-   * @returns {Array} Returns `array`.
-   */
-  function copyArray(source, array) {
-    var index = -1,
-        length = source.length;
-
-    array || (array = Array(length));
-    while (++index < length) {
-      array[index] = source[index];
-    }
-    return array;
-  }
-
-  /**
-   * Copies properties of `source` to `object`.
-   *
-   * @private
-   * @param {Object} source The object to copy properties from.
-   * @param {Array} props The property names to copy.
-   * @param {Object} [object={}] The object to copy properties to.
-   * @returns {Object} Returns `object`.
-   */
-  function copyObject(source, props, object) {
-    return copyObjectWith(source, props, object);
-  }
-
-  /**
-   * This function is like `copyObject` except that it accepts a function to
-   * customize copied values.
-   *
-   * @private
-   * @param {Object} source The object to copy properties from.
-   * @param {Array} props The property names to copy.
-   * @param {Object} [object={}] The object to copy properties to.
-   * @param {Function} [customizer] The function to customize copied values.
-   * @returns {Object} Returns `object`.
-   */
-  function copyObjectWith(source, props, object, customizer) {
-    object || (object = {});
-
-    var index = -1,
-        length = props.length;
-
-    while (++index < length) {
-      var key = props[index],
-          newValue = customizer ? customizer(object[key], source[key], key, object, source) : source[key];
-
-      assignValue(object, key, newValue);
-    }
-    return object;
-  }
-
   /**
    * Used by `_.deburr` to convert latin-1 supplementary letters to basic latin letters.
    *
@@ -2113,6 +2019,21 @@
 
     /*------------------------------------------------------------------------*/
 
+    /**
+     * This function is like `assignValue` except that it doesn't assign `undefined` values.
+     *
+     * @private
+     * @param {Object} object The object to modify.
+     * @param {string} key The key of the property to assign.
+     * @param {*} value The value to assign.
+     */
+    function assignMergeValue(object, key, value) {
+      if ((value !== undefined && !eq(value, object[key])) ||
+          (typeof key == 'number' && value === undefined && !(key in object))) {
+        object[key] = value;
+      }
+    }
+
     /**
      * Assigns own symbol properties of `source` to `object`.
      *
@@ -2133,6 +2054,25 @@
       return object;
     }
 
+    /**
+     * Assigns `value` to `key` of `object` if the existing value is not equivalent
+     * using [`SameValueZero`](http://ecma-international.org/ecma-262/6.0/#sec-samevaluezero)
+     * for equality comparisons.
+     *
+     * @private
+     * @param {Object} object The object to modify.
+     * @param {string} key The key of the property to assign.
+     * @param {*} value The value to assign.
+     */
+    function assignValue(object, key, value) {
+      var oldValue = object[key];
+      if ((!eq(value, oldValue) ||
+            (eq(oldValue, objectProto[key]) && !hasOwnProperty.call(object, key))) ||
+          (value === undefined && !(key in object))) {
+        object[key] = value;
+      }
+    }
+
     /**
      * Removes `key` and its value from the associative array.
      *
@@ -3564,7 +3504,7 @@
         value = array[index],
         computed = iteratee ? iteratee(value) : value;
 
-        if ((seen === seen ? (seen !== computed) : (computed === computed))) {
+        if (!eq(seen, computed)) {
           seen = computed;
           result[++resIndex] = value;
         }
@@ -3870,6 +3810,64 @@
       return result;
     }
 
+    /**
+     * Copies the values of `source` to `array`.
+     *
+     * @private
+     * @param {Array} source The array to copy values from.
+     * @param {Array} [array=[]] The array to copy values to.
+     * @returns {Array} Returns `array`.
+     */
+    function copyArray(source, array) {
+      var index = -1,
+          length = source.length;
+
+      array || (array = Array(length));
+      while (++index < length) {
+        array[index] = source[index];
+      }
+      return array;
+    }
+
+    /**
+     * Copies properties of `source` to `object`.
+     *
+     * @private
+     * @param {Object} source The object to copy properties from.
+     * @param {Array} props The property names to copy.
+     * @param {Object} [object={}] The object to copy properties to.
+     * @returns {Object} Returns `object`.
+     */
+    function copyObject(source, props, object) {
+      return copyObjectWith(source, props, object);
+    }
+
+    /**
+     * This function is like `copyObject` except that it accepts a function to
+     * customize copied values.
+     *
+     * @private
+     * @param {Object} source The object to copy properties from.
+     * @param {Array} props The property names to copy.
+     * @param {Object} [object={}] The object to copy properties to.
+     * @param {Function} [customizer] The function to customize copied values.
+     * @returns {Object} Returns `object`.
+     */
+    function copyObjectWith(source, props, object, customizer) {
+      object || (object = {});
+
+      var index = -1,
+          length = props.length;
+
+      while (++index < length) {
+        var key = props[index],
+            newValue = customizer ? customizer(object[key], source[key], key, object, source) : source[key];
+
+        assignValue(object, key, newValue);
+      }
+      return object;
+    }
+
     /**
      * Creates a function like `_.groupBy`.
      *
@@ -4938,8 +4936,7 @@
       if (type == 'number'
           ? (isArrayLike(object) && isIndex(index, object.length))
           : (type == 'string' && index in object)) {
-        var other = object[index];
-        return value === value ? (value === other) : (other !== other);
+        return eq(value, object[index]);
       }
       return false;
     }
@@ -6274,8 +6271,7 @@
       var length = array ? array.length : 0;
       if (length) {
         var index = baseSortedIndex(array, value);
-        if (index < length &&
-            (value === value ? (value === array[index]) : (array[index] !== array[index]))) {
+        if (index < length && eq(value, array[index])) {
           return index;
         }
       }
@@ -6342,10 +6338,8 @@
     function sortedLastIndexOf(array, value) {
       var length = array ? array.length : 0;
       if (length) {
-        var index = baseSortedIndex(array, value, true) - 1,
-            other = array[index];
-
-        if (value === value ? (value === other) : (other !== other)) {
+        var index = baseSortedIndex(array, value, true) - 1;
+        if (eq(value, array[index])) {
           return index;
         }
       }