add cpp function

source/scripts/unique-landuse-count.cpp

@@ -0,0 +1,39 @@
+#include <Rcpp.h>
+#include <unordered_set>
+using namespace Rcpp;
+
+// [[Rcpp::export]]
+IntegerVector count_unique_landuse(NumericVector x, size_t ni, size_t nw) {
+    IntegerVector out(ni);
+
+    // loop over cells
+    size_t start = 0;
+    for (size_t i = 0; i < ni; i++) {
+        size_t end = start + nw;
+
+        // Use an unordered_set to automatically handle uniqueness
+        std::unordered_set<int> unique_values;
+        bool all_na = true;
+
+        // loop over the values of a window
+        for (size_t j = start; j < end; j++) {
+            if (!R_IsNA(x[j])) {
+                // insert() only adds the value if it's not already in the set
+                unique_values.insert(static_cast<int>(x[j]));
+                all_na = false;
+            }
+        }
+
+        // If all values in the window are NA, set the output to NA
+        // Otherwise, set it to the count of unique values
+        if (all_na) {
+            out[i] = NA_INTEGER;
+        } else {
+            out[i] = unique_values.size();
+        }
+
+        start = end;
+    }
+
+    return out;
+}