Added group_by function

Author: SanjayBoricha

index.js

@@ -485,6 +485,21 @@ function find_key_and_update(arr, parent_key, parent_value, target_key, target_v
     return arr;
 }
 
+/**
+ * Group by key in array of object
+ * 
+ * @param array arr
+ * @param string key
+ * @returns object
+ */
+function group_by(arr, key) {
+    is_array(arr)
+    return arr.reduce(function (rv, x) {
+        (rv[x[key]] = rv[x[key]] || []).push(x);
+        return rv;
+    }, {});
+}
+
 export {
     is_array,
     is_num_array,
@@ -512,4 +527,5 @@ export {
     get_rms_value,
     find_key_and_update,
     find_and_update,
+    group_by,
 };