Changeset: 5be0f60d8000 for MonetDB
URL: http://dev.monetdb.org/hg/MonetDB?cmd=changeset;node=5be0f60d8000
Modified Files:
gdk/gdk_group.c
Branch: Feb2013
Log Message:
More efficient algorithm to subgroup sorted values.
See the comments for an explanation of the algorithm.
diffs (108 lines):
diff --git a/gdk/gdk_group.c b/gdk/gdk_group.c
--- a/gdk/gdk_group.c
+++ b/gdk/gdk_group.c
@@ -392,10 +392,16 @@ BATgroup_internal(BAT **groups, BAT **ex
*groups = gn;
} else if (b->tsorted || b->trevsorted) {
BUN i, j;
+ BUN *pgrp;
/* for each value, we need to scan all previous equal
* values (a consecutive, possibly empty, range) to
- * see if we can find one in the same old group */
+ * see if we can find one in the same old group
+ *
+ * we do this by maintaining for each old group the
+ * last time we saw that group, so if the last time we
+ * saw the old group of the current value is within
+ * this range, we can reuse the new group */
ALGODEBUG fprintf(stderr, "#BATgroup(b=%s#" BUNFMT ","
"g=%s#" BUNFMT ","
"e=%s#" BUNFMT ","
@@ -406,12 +412,32 @@ BATgroup_internal(BAT **groups, BAT **ex
e ? BATgetId(e) : "NULL", e ? BATcount(e) : 0,
h ? BATgetId(h) : "NULL", h ? BATcount(h) : 0,
subsorted);
+ /* determine how many old groups there are */
+ if (e) {
+ j = BATcount(e) + (BUN) e->hseqbase;
+ } else if (h) {
+ j = BATcount(h) + (BUN) h->hseqbase;
+ } else {
+ oid m = 0;
+ for (i = 0, j = BATcount(g); i < j; i++)
+ if (grps[i] > m)
+ m = grps[i];
+ j = (BUN) m + 1;
+ }
+ /* array to maintain last time we saw each old group */
+ pgrp = GDKmalloc(sizeof(BUN) * j);
+ if (pgrp == NULL)
+ goto error;
+ /* initialize to impossible position */
+ memset(pgrp, ~0, sizeof(BUN) * j);
+
pv = BUNtail(bi, BUNfirst(b));
ngrps[0] = ngrp;
if (extents)
exts[0] = b->hseqbase;
if (histo)
cnts[0] = 1;
+ pgrp[grps[0]] = BUNfirst(b);
ngrp++; /* the next group to be assigned */
gn->tsorted = 1; /* be optimistic */
for (j = r = BUNfirst(b), p = r + 1, q = r + BATcount(b);
@@ -419,21 +445,25 @@ BATgroup_internal(BAT **groups, BAT **ex
p++) {
v = BUNtail(bi, p);
if (cmp(v, pv) == 0) {
- /* range [j, p) is all same value,
- * find one in the same group */
- for (i = j; i < p; i++) {
- if (grps[i - r] == grps[p - r]) {
- oid grp = ngrps[i - r];
- ngrps[p - r] = grp;
- if (histo)
- cnts[grp]++;
- if (gn->tsorted &&
- grp != ngrp - 1)
- gn->tsorted = 0;
- break;
- }
- }
- if (i < p) {
+ /* range [j, p) is all same value */
+ /* i is position where we saw p's old
+ * group last */
+ i = pgrp[grps[p - r]];
+ /* p is new position where we saw this
+ * group */
+ pgrp[grps[p - r]] = p;
+ if (j <= i && i < p) {
+ /* i is position of equal
+ * value in same old group as
+ * p, so p gets same new group
+ * as i */
+ oid grp = ngrps[i - r];
+ ngrps[p - r] = grp;
+ if (histo)
+ cnts[grp]++;
+ if (gn->tsorted &&
+ grp != ngrp - 1)
+ gn->tsorted = 0;
/* we found the value/group
* combination, go to next
* value */
@@ -443,10 +473,12 @@ BATgroup_internal(BAT **groups, BAT **ex
/* value differs from previous value */
j = p;
pv = v;
+ pgrp[grps[p - r]] = p;
}
/* start a new group */
GRPnotfound();
}
+ GDKfree(pgrp);
} else if (b->T->hash) {
/* we already have a hash table on b */
ALGODEBUG fprintf(stderr, "#BATgroup(b=%s#" BUNFMT ","
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