[c++] Add Feature filter template

Author: mpsonntag

src/filters.h

@@ -74,4 +74,25 @@ std::vector<T> filterEntity(const extractor &input, FN ff) {
     return res;
 }
 
+template<typename T, typename FN>
+std::vector<T> filterFeature(const extractor &input, FN ff) {
+    std::vector<T> res;
+
+    switch (input.num<uint8_t>(2)) {
+    case switchFilter::AcceptAll:
+        res = ff(nix::util::AcceptAll<T>());
+        break;
+    case switchFilter::Id:
+        res = ff(nix::util::IdFilter<T>(input.str(3)));
+        break;
+    case switchFilter::Ids:
+        // this will crash matlab, if its not a vector of strings...
+        res = ff(nix::util::IdsFilter<T>(input.vec<std::string>(3)));
+        break;
+    default: throw std::invalid_argument("unknown or unsupported filter");
+    }
+
+    return res;
+}
+
 #endif