diff --git a/.idea/jsLibraryMappings.xml b/.idea/jsLibraryMappings.xml
deleted file mode 100644
index 72f49aa..0000000
--- a/.idea/jsLibraryMappings.xml
+++ /dev/null
@@ -1,7 +0,0 @@
-<?xml version="1.0" encoding="UTF-8"?>
-<project version="4">
-  <component name="JavaScriptLibraryMappings">
-    <file url="file://$PROJECT_DIR$/packages/backend" libraries="{Node.js Core}" />
-    <file url="file://$PROJECT_DIR$/packages/frontend" libraries="{Node.js Core}" />
-  </component>
-</project>
\ No newline at end of file
diff --git a/packages/backend/src/util/functions.ts b/packages/backend/src/util/functions.ts
index 852bc5c..5f28d65 100644
--- a/packages/backend/src/util/functions.ts
+++ b/packages/backend/src/util/functions.ts
@@ -1,4 +1,42 @@
+/*
+ * Copyright (C) 2024 Aleksander <alekswilc> Wilczyński (aleks@alekswilc.dev)
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU Affero General Public License as published
+ * by the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU Affero General Public License for more details.
+ *
+ * See LICENSE for more.
+ */
+
+// TODO: typings
+export const removeProperties = <T>(data: any, names: string[]) =>
+{
+    for (const name of names)
+    {
+        delete data[ name ];
+    }
+    return data as T;
+};
+
+
 // https://stackoverflow.com/questions/3446170/escape-string-for-use-in-javascript-regex
 export const escapeRegexString = (str: string) => {
     return str.replace(/[.*+?^${}()|[\]\\]/g, '\\$&');
-}
\ No newline at end of file
+}
+
+export const isTruthyAndGreaterThanZero = (data: number) => {
+    if (!data) return false;
+    return data > 0;
+}
+
+export const arrayGroupBy = <T>(array: T[], predicate: (value: T, index: number, array: T[]) => string) =>
+    Object.values((array.reduce((acc, value, index, array) => {
+        (acc[predicate(value, index, array)] ||= []).push(value);
+        return acc;
+    }, {} as { [key: string]: T[] }))).flat();
\ No newline at end of file