code: public static ConcatVectorNamespace readFromProto(ConcatVectorNamespaceProto.ConcatVectorNamespace m) {
          ConcatVectorNamespace namespace = new ConcatVectorNamespace();
  
          for (ConcatVectorNamespaceProto.ConcatVectorNamespace.FeatureToIndexComponent component : m.getFeatureToIndexList()) {
              namespace.featureToIndex.put(component.getKey(), component.getData());
          }
  
          for (ConcatVectorNamespaceProto.ConcatVectorNamespace.SparseFeatureIndex sparseFeature : m.getSparseFeatureIndexList()) {
              String key = sparseFeature.getKey();
              ObjectIntMap<String> sparseMap = new ObjectIntHashMap<>();
              IntObjectMap<String> reverseSparseMap = new IntObjectHashMap<>();
              for (ConcatVectorNamespaceProto.ConcatVectorNamespace.FeatureToIndexComponent component : sparseFeature.getFeatureToIndexList()) {
                  sparseMap.put(component.getKey(), component.getData());
                  reverseSparseMap.put(component.getData(), component.getKey());
              }
              namespace.sparseFeatureIndex.put(key, sparseMap);
              namespace.reverseSparseFeatureIndex.put(key, reverseSparseMap);
          }
  
          return namespace;
      }
docs: Recreates an in-memory concat vector object from a Proto serialization.
  
  @param m the concat vector proto
  @return an in-memory concat vector object