add proton decay event labelling

pynuml/labels/__init__.py

@@ -1,3 +1,4 @@
 from .standard import StandardLabels
 from .simple import SimpleLabels
-from .flavor import FlavorLabels
+from .flavor import FlavorLabels
+from .pdk import PDKLabels

pynuml/labels/pdk.py

@@ -0,0 +1,33 @@
+import pandas as pd
+
+class PDKLabels:
+    def __init__(self):
+        self._labels = ('nu', 'pdk')
+
+    @property
+    def labels(self):
+        return self._labels
+
+    def label(self, idx: int):
+        if not 0 <= label < len(self._labels):
+            raise Exception(f'index {idx} out of range for {len(self._labels)} labels.')
+        return self._labels[idx]
+
+    def index(self, name: str):
+        if name not in self._labels:
+            raise Exception(f'"{name}" is not the name of a class.')
+        return self._labels.index(name)
+
+    @property
+    def nu(self):
+        return self.index('nu')
+
+    @property
+    def pdk(self):
+        return self.index('pdk')
+
+    def __call__(self, event: pd.Series):
+        if 12 <= abs(event.nu_pdg) <= 16:
+            return self.nu
+        else:
+            return self.pdk