Move internal modules to “internal” folder.

.internal/basePickBy.js

@@ -0,0 +1,29 @@
+import baseGet from './.internal/baseGet.js';
+import baseSet from './.internal/baseSet.js';
+import castPath from './.internal/castPath.js';
+
+/**
+ * The base implementation of  `pickBy`.
+ *
+ * @private
+ * @param {Object} object The source object.
+ * @param {string[]} paths The property paths to pick.
+ * @param {Function} predicate The function invoked per property.
+ * @returns {Object} Returns the new object.
+ */
+function basePickBy(object, paths, predicate) {
+  let index = -1;
+  const length = paths.length;
+  const result = {};
+
+  while (++index < length) {
+    const path = paths[index];
+    const value = baseGet(object, path);
+    if (predicate(value, path)) {
+      baseSet(result, castPath(path, object), value);
+    }
+  }
+  return result;
+}
+
+export default basePickBy;