Fix issue #5

Initialize prev_end with smallest possible value and then count upwards

src/cluster_interval.cpp

@@ -98,8 +98,8 @@ IntegerVector cluster_interval(NumericVector starts, NumericVector ends, int max
   // The implementation is inspired by the bedtools implementation:
   // https://github.com/arq5x/bedtools2/blob/14fbbb8aed5c6a04685da2cee3f11b98d70304a7/src/clusterBed/clusterBed.cpp
   IntegerVector result(starts.size());
-  int cluster_id = 0;
-  int prev_end = starts[0];
+  int cluster_id = -1;
+  int prev_end = std::numeric_limits<int>::min();
   vector<int> indices = sort_indices<true>(as<std::vector<double> >(starts));
   for (int j = 0; j < indices.size(); j++) {
     int i = indices[j];

tests/testthat/test_cluster.R

@@ -29,4 +29,10 @@ test_that("cluster_interval works", {
   starts <- c(50, 100, 120, 180, 350)
   ends <- c(75, 200, 150, 210, 400)
   expect_equal(cluster_interval(starts, ends), c(0,1,1,1,2))
+
+  starts <- c(500, 300, 150)
+  ends <- c(510, 310, 160)
+  expect_equal(cluster_interval(start, end), c(2,1,0))
+
+  expect_equal(cluster_interval(numeric(0), numeric(0)), numeric(0))
 })