Adds function to concatenate runs along trainId dimension

Load.py

@@ -449,3 +449,20 @@ def load(fields, runNB, proposalNB, semesterNB, topic='SCS', display=False,
     result.attrs['run'] = run
     result.attrs['runFolder'] = runFolder
     return result
+
+def concatenateRuns(runs):
+    """ Concatenate two runs with identical data variables along the trainId dimension
+        Input:
+            runs: (list) the xarray Datasets to concatenate
+        Output:
+            a concatenated xarray Dataset
+    """
+    keys = runs[0].keys()
+    for run in runs[1:]:
+        if run.keys() != keys:
+            print('data fields between different runs are not identical. Cannot combine runs.')
+            return
+    
+    result = xr.concat(runs, dim='trainId')
+    result = result.sortby(result.trainId)
+    return result