Changeset: aa55f169d4cd for MonetDB
URL: https://dev.monetdb.org/hg/MonetDB?cmd=changeset;node=aa55f169d4cd
Modified Files:
gdk/gdk_firstn.c
Branch: Jul2017
Log Message:
Add some comments.
diffs (32 lines):
diff --git a/gdk/gdk_firstn.c b/gdk/gdk_firstn.c
--- a/gdk/gdk_firstn.c
+++ b/gdk/gdk_firstn.c
@@ -119,6 +119,10 @@
* refer to the N smallest/largest (depending on asc) tail values of b
* (taking the optional candidate list s into account). If there are
* multiple equal values to take us past N, we return a subset of those.
+ *
+ * If lastp is non-NULL, it is filled in with the oid of the "last"
+ * value, i.e. the value of which there may be multiple occurrences
+ * that are not all included in the first N.
*/
static BAT *
BATfirstn_unique(BAT *b, BAT *s, BUN n, int asc, oid *lastp)
@@ -370,6 +374,17 @@ BATfirstn_unique(BAT *b, BAT *s, BUN n,
} \
} while (0)
+/* This version of BATfirstn is like the one above, except that it
+ * also looks at groups. The values of the group IDs are important:
+ * we return only the smallest N (i.e., not dependent on asc which
+ * refers only to the values in the BAT b).
+ *
+ * If lastp is non-NULL, it is filled in with the oid of the "last"
+ * value, i.e. the value of which there may be multiple occurrences
+ * that are not all included in the first N. If lastgp is non-NULL,
+ * it is filled with the group ID (not the oid of the group ID) for
+ * that same value.
+ */
static BAT *
BATfirstn_unique_with_groups(BAT *b, BAT *s, BAT *g, BUN n, int asc, oid
*lastp, oid *lastgp)
{
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