Added function to load data for multiply MDSystem

src/mdevaluate/system.py

@@ -42,3 +42,15 @@ class MDSystem(abc.ABC):
             ]
         )
         run(["mv", hdf5_temp_file, hdf5_file])
+
+
+def load_and_concat_data(systems: list[MDSystem], key: str, verbose: bool = False):
+    data = []
+    for system in systems:
+        try:
+            data.append(system.load_results(key=key))
+            if verbose:
+                print(f"Load {system}")
+        except (FileNotFoundError, KeyError):
+            continue
+    return pd.concat(data, ignore_index=True)