Changeset: 354674570bd5 for MonetDB
URL: http://dev.monetdb.org/hg/MonetDB?cmd=changeset;node=354674570bd5
Modified Files:
gdk/gdk.h
gdk/gdk_sample.c
Branch: default
Log Message:
BATsample_ implements BATsample but expecting void head and produce oid's of
sampled BUNs.
diffs (89 lines):
diff --git a/gdk/gdk.h b/gdk/gdk.h
--- a/gdk/gdk.h
+++ b/gdk/gdk.h
@@ -3165,6 +3165,7 @@ gdk_export BAT *BATintersectcand(BAT *a,
*
*/
gdk_export BAT *BATsample(BAT *b, BUN n);
+gdk_export BAT *BATsample_(BAT *b, BUN n); /* version that expects void head
and returns oids */
/* generic n-ary multijoin beast, with defines to interpret retval */
#define MULTIJOIN_SORTED(r) ((char*) &r)[0]
diff --git a/gdk/gdk_sample.c b/gdk/gdk_sample.c
--- a/gdk/gdk_sample.c
+++ b/gdk/gdk_sample.c
@@ -114,3 +114,74 @@ bunins_failed:
BBPreclaim(bn);
return NULL;
}
+
+/* BATsample_ implements sampling for void headed BATs */
+BAT *
+BATsample_(BAT *b, BUN n)
+{
+ BAT *bn;
+ BUN cnt;
+
+ BATcheck(b, "BATsample");
+ assert(BAThdense(b));
+ ERRORcheck(n > BUN_MAX, "BATsample: sample size larger than BUN_MAX\n");
+ ALGODEBUG fprintf(stderr, "#BATsample: sample " BUNFMT " elements.\n",
n);
+
+ cnt = BATcount(b);
+ /* empty sample size */
+ if (n == 0) {
+ bn = BATnew(TYPE_void, TYPE_void, 0);
+ BATsetcount(bn, 0);
+ BATseqbase(bn, 0);
+ BATseqbase(BATmirror(bn), 0);
+ /* sample size is larger than the input BAT, return all oids */
+ } else if (cnt <= n) {
+ bn = BATnew(TYPE_void, TYPE_void, cnt);
+ BATsetcount(bn, cnt);
+ BATseqbase(bn, 0);
+ BATseqbase(BATmirror(bn), b->H->seq);
+ } else {
+ BUN smp = 0;
+ /* we use wrd and not BUN since p may be -1 */
+ wrd top = b->hseqbase + cnt - n;
+ wrd p = ((wrd) b->hseqbase) - 1;
+ oid *o;
+ bn = BATnew(TYPE_void, TYPE_oid, smp);
+ if (bn == NULL) {
+ GDKerror("#BATsample: memory allocation error");
+ return NULL;
+ }
+ o = (oid *) Tloc(bn, BUNfirst(bn));
+ while (smp < n-1) { /* loop until all but 1 values are sampled
*/
+ double v = DRAND;
+ double quot = (double)top/(double)cnt;
+ BUN jump = 0;
+ while (quot > v) { /* determine how many positions to
jump */
+ jump++;
+ top--;
+ cnt--;
+ quot *= (double)top/(double)cnt;
+ }
+ p += (jump+1);
+ cnt--;
+ o[smp++] = (oid) p;
+ }
+ /* 1 left */
+ p += (BUN) rand() % cnt;
+ o[smp] = (oid) p;
+
+ /* property management */
+ BATsetcount(bn, n);
+ bn->trevsorted = bn->U->count <= 1;
+ bn->tkey = 1;
+ bn->tdense = bn->U->count <= 1;
+ if (bn->U->count == 1)
+ bn->tseqbase = * (oid *) Tloc(bn, BUNfirst(bn));
+ bn->hdense = 1;
+ bn->hseqbase = 0;
+ bn->hkey = 1;
+ bn->hrevsorted = bn->U->count <= 1;
+ }
+
+ return bn;
+}
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