Add sum filter

src/anemoi/datasets/create/functions/filters/sum.py

@@ -0,0 +1,71 @@
+# (C) Copyright 2024 Anemoi contributors.
+#
+# This software is licensed under the terms of the Apache Licence Version 2.0
+# which can be obtained at http://www.apache.org/licenses/LICENSE-2.0.
+#
+# In applying this licence, ECMWF does not waive the privileges and immunities
+# granted to it by virtue of its status as an intergovernmental organisation
+# nor does it submit to any jurisdiction.
+
+
+from collections import defaultdict
+
+from earthkit.data.indexing.fieldlist import FieldArray
+
+
+class NewDataField:
+    def __init__(self, field, data, new_name):
+        self.field = field
+        self.data = data
+        self.new_name = new_name
+
+    def to_numpy(self, *args, **kwargs):
+        return self.data
+
+    def metadata(self, key=None, **kwargs):
+        if key is None:
+            return self.field.metadata(**kwargs)
+
+        value = self.field.metadata(key, **kwargs)
+        if key == "param":
+            return self.new_name
+        return value
+
+    def __getattr__(self, name):
+        return getattr(self.field, name)
+
+
+def execute(context, input, params, output):
+    """Computes the sum over a set of variables"""
+    result = FieldArray()
+
+    needed_fields = defaultdict(dict)
+
+    for f in input:
+        key = f.metadata(namespace="mars")
+        param = key.pop("param")
+        if param in params:
+            key = tuple(key.items())
+
+            if param in needed_fields[key]:
+                raise ValueError(f"Duplicate field {param} for {key}")
+
+            needed_fields[key][param] = f
+        else:
+            result.append(f)
+
+    for keys, values in needed_fields.items():
+
+        if len(values) != len(params):
+            raise ValueError("Missing fields")
+
+        s = None
+        for k, v in values.items():
+            c = v.to_numpy(flatten=True)
+            if s is None:
+                s = c
+            else:
+                s += c
+        result.append(NewDataField(values[list(values.keys())[0]], s, output))
+
+    return result