chore(*): Improve scroll and pipe performance.

Author: MKirova

projects/igniteui-angular/src/lib/data-operations/merge-strategy.ts

@@ -75,7 +75,7 @@ export class DefaultMergeStrategy implements IGridMergeStrategy {
                 index++;
                 continue;
             }
-            const recToUpdateData = recData ?? { recordRef: grid.isGhostRecord(rec) ? rec.recordRef : rec, cellMergeMeta: new Map<string, IMergeByResult>(), ghostRecord: rec.ghostRecord };
+            const recToUpdateData = recData ?? { recordRef: grid.isGhostRecord(rec) ? rec.recordRef : rec, cellMergeMeta: new Map<string, IMergeByResult>(), ghostRecord: rec.ghostRecord, index: index };
             recToUpdateData.cellMergeMeta.set(field, { rowSpan: 1, childRecords: [] });
             if (prev && comparer.call(this, prev.recordRef, recToUpdateData.recordRef, field, isDate, isTime) && prev.ghostRecord === recToUpdateData.ghostRecord) {
                 const root = prev.cellMergeMeta.get(field)?.root ?? prev;

projects/igniteui-angular/src/lib/grids/grid-base.directive.ts

@@ -8241,16 +8241,16 @@ export abstract class IgxGridBaseDirective implements GridType,
         // recalc merged data
         if (this.columnsToMerge.length > 0) {
             const startIndex = this.verticalScrollContainer.state.startIndex;
-            const prevDataView = this.verticalScrollContainer.igxForOf?.slice(0, startIndex);
             const data = [];
-            for (let index = 0; index < startIndex; index++) {
-                const rec = prevDataView[index];
-                if (rec.cellMergeMeta &&
-                    // index + maxRowSpan is within view
-                    startIndex < (index + Math.max(...rec.cellMergeMeta.values().toArray().map(x => x.rowSpan)))) {
-                    const visibleIndex = this.isRowPinningToTop ? index + this.pinnedRecordsCount : index;
-                    data.push({ record: rec, index: visibleIndex, dataIndex: index });
-                }
+            const rec = this.verticalScrollContainer.igxForOf[startIndex];
+            if (rec && rec.cellMergeMeta) {
+                this.columnsToMerge.forEach((col) => {
+                    const root = rec.cellMergeMeta.get(col.field).root;
+                    if (root) {
+                        data.push({ record: root, index: root.index, dataIndex: root.index });
+                    }
+                })
+
             }
             this._mergedDataInView = data;
             this.notifyChanges();

projects/igniteui-angular/src/lib/grids/grid/grid.pipes.ts

@@ -131,7 +131,7 @@ export class IgxGridUnmergeActivePipe implements PipeTransform {
         }
         let result = cloneArray(collection) as any;
         uniqueRoots.forEach(x => {
-            const index = result.indexOf(x);
+            const index = x.index;
             const colKeys = [...x.cellMergeMeta.keys()];
             const cols = colsToMerge.filter(col => colKeys.indexOf(col.field) !== -1);
             let res = [];