[nstepien]

TreeDataGrid no longer asks for a function that groups a set of rows into a Record<string, readonly R[]>. Instead, getRowGroupKey(row, columnKey) returns the group key of a single row, and the grid builds the group tree itself.

-  rowGrouper: (rows: readonly R[], columnKey: string) => Record<string, readonly R[]>;
+  getRowGroupKey?: Maybe<(row: R, columnKey: string) => string>;

The new prop is optional. It defaults to String(row[columnKey]), so grouping now only requires groupBy, expandedGroupIds, and onExpandedGroupIdsChange:

 <TreeDataGrid
   groupBy={['country', 'year']}
-  rowGrouper={rowGrouper}
   expandedGroupIds={expandedGroupIds}
   onExpandedGroupIdsChange={setExpandedGroupIds}
 />
-
-function rowGrouper(rows: readonly Row[], columnKey: string) {
-  return Object.groupBy(rows, (row) => row[columnKey]);
-}

Pass it to group on something other than the raw cell value, e.g., bucketing dates by year.

Implementation

• Rows are grouped in a single pass: each row walks the groupBy keys and is added to every group along its path, so a group's childRows holds all of its descendant rows, same as what rowGrouper used to receive at each level.
• Removed the now-dead GroupBy, GroupByMap, and ReadonlyGroupByMap types, and isReadonlyArray.

Memoization

• Grouping and flattening are separate memos. Grouping depends on rows, groupBy, and getRowGroupKey only, so expanding or collapsing a group no longer re-groups every row.
• startRowIndex and the total row count don't depend on the expanded state either, so they're computed while grouping. Flattening now only walks expanded groups: collapsed subtrees are never traversed, and getGroupId is only called for visible groups.
• isGroupRow is a module-level function backed by a module-level WeakSet, since group rows are only ever created by TreeDataGrid. It's stable across renders, so it's out of four dependency arrays and rowHeight survives a toggle.

Breaking changes

groupIdGetter is renamed to getGroupId, as function props are moving to getX names.

Groups are now ordered by the first row that belongs to them. Object.entries() previously sorted integer-like group keys numerically, so a numeric group key over unsorted rows will now come out in row order instead of ascending. A new test covers this, and the row grouping demo now sorts its rows by year within each country so its year groups stay in ascending order.

Notes

vp run ci passes. The existing TreeDataGrid tests now run against the default getRowGroupKey, with dedicated tests covering a custom one and the group order. Visual tests were not run locally; test/visual/treeGrid.test.tsx groups rows that are already in order, so the screenshot is expected to be unchanged.

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Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 98.57%. Comparing base (e630880) to head (3bf6c5e).

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #4159   +/-   ##
=======================================
  Coverage   98.56%   98.57%           
=======================================
  Files          45       45           
  Lines        1957     1962    +5     
  Branches      728      731    +3     
=======================================
+ Hits         1929     1934    +5     
  Misses         28       28           

Files with missing lines	Coverage Δ
src/TreeDataGrid.tsx	94.59% <100.00%> (+0.15%)	⬆️

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[nstepien]

@amanmahajan7 any issues with replacing rowGrouper with the optional getRowGroupKey prop?
groupIdGetter is also renamed to getGroupId.

I also want to rename rowKeyGetter to getRowGet in a future PR, so this is a precursor to it.