Rename mapKeys and mapValues to mapKey and mapValue.

mapKey.js

@@ -0,0 +1,30 @@
+import baseAssignValue from './.internal/baseAssignValue.js'
+
+/**
+ * The opposite of `mapValue` this method creates an object with the
+ * same values as `object` and keys generated by running each own enumerable
+ * string keyed property of `object` thru `iteratee`. The iteratee is invoked
+ * with three arguments: (value, key, object).
+ *
+ * @since 3.8.0
+ * @category Object
+ * @param {Object} object The object to iterate over.
+ * @param {Function} iteratee The function invoked per iteration.
+ * @returns {Object} Returns the new mapped object.
+ * @see mapValues
+ * @example
+ *
+ * mapKey({ 'a': 1, 'b': 2 }, function(value, key) {
+ *   return key + value
+ * })
+ * // => { 'a1': 1, 'b2': 2 }
+ */
+function mapKey(object, iteratee) {
+  const result = {}
+  Object.keys(object).forEach((value, key, object) => {
+    baseAssignValue(result, iteratee(value, key, object), value)
+  })
+  return result
+}
+
+export default mapKeys