3 files changed, 91 insertions, 2 deletions

diff --git a/km-rand.c b/km-rand.c
index fcc6a74..1410861 100644
--- a/km-rand.c
+++ b/km-rand.c
@@ -12,6 +12,16 @@ km_rand_fill(
   return rs->cbs->fill(rs, num_floats, floats);
 }
 
+// fill buffer with N random size_ts
+bool
+km_rand_fill_sizes(
+  km_rand_t * const rs,
+  const size_t num_sizes,
+  size_t * const sizes
+) {
+  return rs->cbs->fill_sizes(rs, num_sizes, sizes);
+}
+
 // finalize random source
 void
 km_rand_fini(
@@ -40,11 +50,30 @@ system_on_fill(
   return true;
 }
 
+// fill sizes callback for system random source
+static bool
+system_on_fill_sizes(
+  km_rand_t * const rs,
+  const size_t num_sizes,
+  size_t * const sizes
+) {
+  UNUSED(rs);
+
+  // generate random size_ts
+  for (size_t i = 0; i < num_sizes; i++) {
+    sizes[i] = rand();
+  }
+
+  // return success
+  return true;
+}
+
 // system random source callbacks
 static const km_rand_cbs_t
 SYSTEM_CBS = {
-  .fill = system_on_fill,
-  .fini = NULL,
+  .fill       = system_on_fill,
+  .fill_sizes = system_on_fill_sizes,
+  .fini       = NULL,
 };
 
 // init system random source (uses system rand())
diff --git a/km-set.c b/km-set.c
index 37a7337..535b46b 100644
--- a/km-set.c
+++ b/km-set.c
@@ -301,3 +301,50 @@ km_set_init_rand_clusters(
   // add data, return result
   return km_set_push(cs, num_clusters, floats, ints);
 }
+
+// init a set with num_clusters clusters of shape num_floats by picking
+// random initial points from the set
+bool
+km_set_init_rand_points(
+  km_set_t * const cs,
+  const km_set_t * const set,
+  const size_t num_clusters,
+  km_rand_t * const rs
+) {
+  const size_t num_floats = set->shape.num_floats,
+               stride = sizeof(float) * num_floats;
+
+  // init cluster shape
+  const km_shape_t shape = {
+    .num_floats = num_floats,
+    .num_ints = 1,
+  };
+
+  // get random row offsets
+  size_t rows[num_clusters];
+  if (!km_rand_fill_sizes(rs, num_clusters, rows)) {
+    // return failure
+    return false;
+  }
+
+  // generate random cluster centers
+  float floats[num_floats * num_clusters];
+  for (size_t i = 0; i < num_clusters; i++) {
+    const size_t row_num = rows[i] % set->num_rows;
+    const float * const row_floats = km_set_get_row(set, row_num);
+    memcpy(floats + i * num_floats, row_floats, stride);
+  }
+
+  // FIXME: should probably be heap-allocated
+  int ints[num_clusters];
+  memset(ints, 0, sizeof(ints));
+
+  // init cluster set
+  if (!km_set_init(cs, &shape, num_clusters)) {
+    // return failure
+    return false;
+  }
+
+  // add data, return result
+  return km_set_push(cs, num_clusters, floats, ints);
+}
diff --git a/km.h b/km.h
index 82bd835..c70e13e 100644
--- a/km.h
+++ b/km.h
@@ -11,6 +11,7 @@ typedef struct km_rand_t_ km_rand_t;
 // random number source callbacks
 typedef struct {
   _Bool (*fill)(km_rand_t * const, const size_t, float * const);
+  _Bool (*fill_sizes)(km_rand_t * const, const size_t, size_t * const);
   void (*fini)(km_rand_t * const);
 } km_rand_cbs_t;
 
@@ -23,6 +24,9 @@ struct km_rand_t_ {
 // fill buffer with N random floats
 _Bool km_rand_fill(km_rand_t * const, const size_t, float * const);
 
+// fill buffer with N random size_ts
+_Bool km_rand_fill_sizes(km_rand_t * const, const size_t, size_t * const);
+
 // finalize random source
 void km_rand_fini(km_rand_t * const);
 
@@ -82,6 +86,15 @@ _Bool km_set_init_rand_clusters(
   km_rand_t *
 );
 
+// init a set with num_clusters clusters of random points from the
+// given set
+_Bool km_set_init_rand_points(
+  km_set_t * const,
+  const km_set_t * const,
+  const size_t,
+  km_rand_t *
+);
+
 typedef struct {
   float d2;
   size_t cluster;